Computer wont turn on at first. Also sometimes reboots.

[efbiaiinzinz]

Hi, I have a strange problem.
When I turn off my PC, I can't turn it on right away.
The thing is that when I press the power button the HDD light flashes on for a little time and after that there's nothing.
No fans turn on, nothings seems to start.
When I wait about 5 minutes and press the power button again, it starts normally (meanwhile pressing power button has no effect).
Also since the startup problem I have been experiancing some random reboots. Few, but still.

Computer's configuration is:
Motherboard: M955G (FSB up to 800 MHz, DDRAM up to 400 MHz, SATA support, up to 8xAGP etc.).
Processor: 2.4GHz Intel Celeron (533 MHz FSB, 256KB cache).
RAM: 1x256MB 333MHz DDRAM
HDD: 1x40GB SATA HDD
Graphics: ATI Radeon 9800SE AIW VIVO 128MB 256bit
400w power supply.

I have checked the switch and all wires seem to be connected so the problem lies somewhere else. (After a delay I can turn on computer even by "hotwireing" it by using a simple cord or by switch: it works both ways)

P.S. I cannot set my AGP speed to 8x because when I do, computer crashes altogether when I run some 3D app.
Currently I'm using 4xAGP and Fastwrite is off.

Have you got any clue what to do, because I don't anymore. :confused:

[hittingrabbit]

could be several problems the first is a possible bad power supply.
secondly it could be the wiring for your buttons are backwards after unplugging your computer check the connection of your power button + and - you can switch them to test if it doesnt light up at all then unplug the machine again and switch them back.
Also in the matter of your 8x graphics mode this may simply be your bios settings make sure you know what memory buss frequency your graphics card operates at and change it appropriatly,check if the correct voltage is set.
core speed is important never over clock the voltage unless your sure that it will be stable as this can burnout your graphics card.
In certain cases ive up'd the voltage on video cards and made the system more stable but thats your call.
If the power supply isnt functioning correctly it will cause random reboots,additionally it may not be providing enough power to your graphic card to operate 8x.