Nasty system crash

[phoenixavatar2]

Hello everyone, I'm hoping I can get some good tech support here for a nasty crash. It started today when I put my foot top of my tower with a little bump. As soon as I did it the image on the monitor froze and stayed there until I restarted. About every five seconds the screen would go black for about a quarter of a second or so. This wasn't a Windows crash, the everything including the mouse and any video in the background instantly stopped. I had audio going at the time and it started playing the last bit of sound for about a tenth of a second, then silence for about a tenth of a second and looping that.Meaning it wasn't a sustained noise, it was stuttering.

I rebooted and continued like normal and it happened again when I bumped the case again a bit later on. This time when I tried to reboot Windows came up in 640x480 and 16-bit color. I rebooted again (did a hard reboot instead of telling Windows to do it like I should have) and it came up normally for about 30 seconds before it crashed again, without me bumping the case, same symptoms as before. I'm going to check all of the connections inside my case but I would like any advice that anyone has before I restart, especially if anyone's run into this.

Here are my system specs:
Asus A8n-SLI Premium mobo
AMD 64 3500+ (Clawhammer) Overclocked to 2.58 Ghz
4x512 sticks of DDR400 RAM
Two Geforce 8600 GTs in SLI (One XFX, the other PNY, unequal clock speeds)
640 gig Sata 2 HDD, the Sata plug has always been a bit loose

I only did the overclocking last week. Only the bus speed has been increased, I couldn't figure out the memory dividers on my BIOS so I left it normal. I've figured that part out now. The second graphics card was only installed Friday and I had no issues using them to play L4D2 for about two hours, along with some other games. It's an old rig and with some games coming out that are pushing it's limits on minimum specs I've been trying to eek out more power on a budget, trying spend just enough to get it running the new things so that when I have the ability to build a brand new one in a few months I won't have wasted too much.

Thanks for any help.

Edit: I ended up getting impatient and booting up again after pushing trying to push the cables in. I've crashed again after about 5 minutes.

 

[phoenixavatar2]

I've tried some new things and now I'm worse off then that I was. I decided to get rid of the overclocking so I went into the BIOS, changed the overclock settings back from manual to auto, saved and tried to load into windows. After the normal bootup stuff before it looks for an OS it just sat there with a blank screen. I rebooted again and nothing happened, the fans turned on but there was a blank screen, no POST beeps. So the next thing I tried was to remove the new video card. I did, remembering to move the SLI selector card back to single and to remove the EZ plug molex and I rebooted. Got a blank screen and the motherboard beeped one long and three short and played the message "System VGA Failure". I had previously forced SLI through the BIOS because it had not auto-detected it so I decided to wipe the CMOS. Did that, same result. Decided to pull my old card from the primary slot and put the new one in. Same result. Plugged the EZ molex back in, same result. I'm at a loss.

 

[phoenixavatar2]

No, but the one I have is only a year old.

 

[phoenixavatar2]

Alright, I pulled out my old 6600GT and put it in, booted right up. So I decided to switch in the 8600s to confirm that they were dead and my original 8600 booted up. So I'm just going to send back the new 8600 and do what I should have done in the first place and gotten an actual video card upgrade instead of trying to screw with SLI.