picked the computer up off the dusty floor....
vacumned it
turned it on, no video.
put in new video card, no video
changed the monitor...np luck
put hard drive in another box, no video
put hard drive back in old computer, no video,
walked by 10 mins. later....video.
shut it down, rebooted, no video.
kept it on all night, shut it off and rebooted, no video
no beeps....
cd and dvd lights flashing/flickering constant, unplugged power to them, no video.
any suggestions, what it may be?

Try turning off your Power Supply and leaving it off for an hour or so, that will surely drain all the remaining power. As I've read using a vacuum cleaner creates static inside electronic components maybe you had static going on and that could be the problem.

It's really hard to diagnose something like that with such information, but of course the first thing that comes to mind is that something was mechanically or electrically disturbed during the process.

If your computer was still plugged-in to AC mains while you were vacuuming, you should know that some circuits still get power and are kept active even when the front panel power-off button is used. That means any shorts that occured with the vacuum nozzle, or by pushing things around while vacuuming could have damaged something.

As for the the "walking by later and the video was on" bit of information, that suggests to me that your system was trying to load the OS, and going through a prolonged error recovery process. There have been times on some of my systems, where if there was a "hiccup" in operation, it could take literally 30 minutes to re-boot as the system tries to recover from the errors. To top that off, I might have to re-boot several times to clear all the errors...an incremental recovery being achieved with each re-boot.


OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

NOTE: all cable/card/drive disconnects should be performed ONLY when the PSU is disconnected from AC mains, and power bled-off. Otherwise, damage to system electronics is possible.

This is the base diagnostic. The basic components you need to get to the BIOS screen are:

PSU, mobo (with CPU), ONE RAM stick, display, video adapter (preferably integrated video but if not available, then a video card). Unplug or remove everything else, including keyboard, mouse, hard drive, CD/DVD, memory card readers, etc.

If when you power-up the system with this minimal configuration the boot screen still does not start to appear, you know at least one major failure is in these few components. Quite often it is the RAM stick. Try a different stick (again, unplug AC mains and bleed power before removing/installing a RAM stick)

At this point, it's a matter of easter-egging for the failing component, but at least you have a very minimal list of suspects.


However, if it DID get to the boot screen, then you can proceed with debugging the additional components. Plug in the keyboard and ensure it will still boot up. If it does...

Then, I'd start with the HDD. If when you connect the HDD it fails to display the boot screen, then your HDD likely has a hardware problem, or your PSU has a power stability problem. But, if the computer gets stuck on or past the boot screen, but doesn't boot into Windows, then the problem is likely corrupt data on the HDD (that's where the protracted recovery times can come to bear on the situation).

Try the above and tell us where you are.