I have a HP Pavillion A6500F with a start up problem that I need some help diagnosing a problem with it or rebuilding it the cheapest way possible.

Problem (1):
Last time I used the computer I noticed it had a software virus on it. The Virus presented itself as an anti virus software that would only allow me to visit its web site to purchase the software.

T/S:
None


Problem (2):
The computer will not boot up to BIOS when turned on. All internal fans power on and run continuously. The DVD powers on and I can hear it spinning. The lights on the USB keyboard flash once and the light on the USB optical mouse flashes once. "No Input detected" displays on the monitor.

T/S:
A
I have rest the BIOS on the mother board by removing the power cord from the power supply then removing the CMOS battery for greater then 30 mins and placing the shorting switch on the #2 and #3 pins then back to the #1 and #2 pins .
B
Used the same monitor with another desktop and functioned fine. Swapped the video output cords back and fourth from VGA and DVI with no different results.
C
Removed the hard drive and plugged it into the working desktop and was able to read the hard drive.
D
Removed the memory sticks and plugged them back in and removed then plugged in most of the cords leading to the MB. Also performed a visual inspection of the MB and did not see anything obviously wrong.

Before this happened to my computer there was a Flip video camera plugged into one of the USB ports on the front of the computer. The computer was in sleep mode and I unplugged it without using safe remove.

I think that the mother board is fried but I am not certain. If it is I would like to rebuild the computer using as much of the existing computer that I can as cheap as possible, it is an old computer after all Thanks.

There used to be a utility on the system boards to do a low level format that I once used to remove a stubborn HD virus, impractical now given the current capacity of the drives. If valid AV software doesn't work a new partition very well might, that however will require a re-install of the OS which means that anything that you HAD on the drive is gone.
If you're not posting at all either the bios and/or the psu is DOA. A new psu MIGHT help. If that fails it usually means you're out a system board.
Outside of the factory any inspection of the system board is mostly a waste of time and effort. As I pointed out in another post, circuit boards of several decades ago might possibly be repairable, now however, you're not just looking at ONE board but at least a board of three layers. Unless you notice an obvious bad/defective cable connection the board is toast.
While the cause of the problems MIGHT be related to the sudden camera disconnect it's moot point now.
Most likely the only reuseable item now is the HD. RAM is a great big maybe. RAM type varies.