Member Avatar for geekwannabe08

Not sure what the problem is...I turned on my computer & it sounded like it was starting up normally (no beeps; prior to Windows startup). The monitor however only displayed the error message "vga--no input signal". I turned off everything, made sure there were no disconnected wires, & unplugged the computer & monitor from the unlimited power supply (ups). Replugged everything together & straight to wall outlet (not ups) & when I turned on the computer again, it seemed to work & Windows came on. Then after about 4 minutes, my cursor froze/optical mouse wasn't responding (light was off the mouse) & keyboard lights were all off & keyboard not working. I tested the computer with a different monitor, & it seemed to work. I wasn't sure if the probem was the first monitor, so I reattached the computer to the first monitor & all was working well. Then, when I shutdown the computer altogether, the three lights on the keyboard (top right) flickered about 10 times then steady green lights remained on. Also, the light on my optical mouse always stays lit & has always been that way (is this normal?).

So my question is, what do you think is faulty...the ups, the monitor, or something else? How can I find out what the problem is & how can it be fixed?

Your help is much appreciated!

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Brief summary and context from the thread: saw a "VGA - no input signal" message while the PC was on an UPS, then the system booted when moved to a wall outlet but later the mouse and keyboard froze; a spare monitor worked during testing; on shutdown the keyboard LEDs blinked several times then stayed lit while the machine was off. focused on the UPS/cable angle and raised hardware possibilities. The behavior points to two separate issues to isolate: intermittent video/signal loss, and peripheral LEDs remaining powered after shutdown.

Practical diagnostic flow to isolate causes:

  • Identify how the keyboard/mouse connect (round PS/2 mini‑DIN vs rectangular USB Type‑A). This determines whether the ports can remain powered while the PC is “off.”
  • With the PC fully shut down, remove AC power (switch off wall/flip PSU or unplug) and confirm whether the keyboard/mouse LEDs go dark. If they do, they were getting standby power; if not, the devices have an independent source (rare).
  • Check BIOS/firmware power options for entries like “USB power in S5”, “Wake on USB/keyboard”, or “ErP/EuP” and try changing them (disable USB power in S5 or enable ErP) to remove standby power.
  • Reproduce the VGA fault with controlled power sources: (a) both PC and monitor on wall, (b) both on UPS, (c) only PC on UPS, monitor on wall. Note exactly which combination triggers the initial “no input” message. That pattern will implicate the UPS vs the PC/video card.
  • If the display loss happens while the system appears to boot, test whether the keyboard works in BIOS (before OS loads) or when running a Live USB. If hardware fails before or inside BIOS, suspect PSU/motherboard/video card hardware; if it fails only in Windows, suspect drivers or power‑management.

If the UPS is implicated, have it tested or replaced; if the fault reproduces on wall power after exhaustive swaps, the likely culprits are PSU standby circuitry, the graphics card, or the motherboard and warrant professional diagnostics. Caution: power down and unplug before opening the case to check cards or connectors, and document which power/combo steps reproduce the fault for any technician.

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Member Avatar for sourcez

When you tried the second monitor and it worked, was that with the UPS?

I'd stick with the other monitor and see whether the problem happens on that one after a while. It doesn't seem quite right that it's all going wrong with a monitor so it would be good to rule that out.

Another thing to check would be whether there's any damage to the VGA cable between the screen and the PC. A shorting cable could cause some small problems and could explain why the first screen was the only one with problems (this is assuming you changed VGA cables when you changed screens!).

Let us know!

Member Avatar for geekwannabe08

Thanks, sourcez!

When I tried the 2nd monitor and it worked, it was without the UPS.

I did use the cable attached already to the 2nd monitor when I tested the computer with the 2nd monitor, so I will see if I can try the 2nd monitor with the original cable, in case that is what's faulty. ...will keep y'all posted.

Member Avatar for geekwannabe08

OK, I can't switch out the cable from my monitor to the computer since it's built-in to the back of the monitor. The monitor, keyboard & mouse seem to be working properly now that I eliminated the ups & instead everything is plugged directly into the wall.

My concern is still this now: the three lights on my keyboard (num lock, caps lock, scroll lock) blink on & off about 10-15 times when I shut down my computer and then they remain lit the entire time my computer is off....ditto for the light on my optical mouse. Why is this happening & should I be concerned??

Member Avatar for sourcez

How are they connected to the computer? Is it PS2 or USB? Is it directly or through a USB hub etc?

If you turn off the power at the wall and wait for the lights to go out; then switch the power back on without powering the pc back up. Do the lights come back on?

Just want to clarify your setup first. :)

Member Avatar for geekwannabe08

The monitor & keyboard are both connected directly to the back of the computer. I think that's what you're asking. There's no other box or contraption between the peripherals & the computer. I don't know exactly what PS2 or USB mean.

Member Avatar for untang

my computer keep on display no VGA: input signal. What should I do?

Member Avatar for jingda

If you have a spare monitor test it out to see whether it is the problem if yes you have to replace it. If no, that means the problems like with the computer. Is it under warranty, if no you might have to remove the case and try some simple repair steps yourself.

1) Reseat the ram sticks
2) Motherboard may be faulty or its battery
3)Take a look at the capacitors on the motherboard and see whether they are bloated. They look like small battery

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