Dell XPS410 with 8600GT

OK, I'm scratching my head here.  Had a display failure during COD play,  desktop went to 4bit 800x600 which I was unable to change, video card unrecognized in the device manager, and on reboot had numbers and slashes (e.g.  1/      1/   1/   1/) all over the screen during boot up and operation (still at low display settings).  Did some tinkering and after multiple attempts, VGA drivers kicked in and desktop was fine (still without recognizing video card).

Reinstalled video drivers and everything worked again.  Then it did the same thing while web browsing (this time with 9/   9/   9/ all over the screen).

I decided to reformat.  During the reformat/reinstall process the numbers and slashes were on the windows blue screen.  Reformattign did not solve anything, still low display levels.  Vidoe card fan still running etc. 

Next, I removed the video card from PCI slot, rebooted to let integrated VGA drivers load for about 20 minutes, shutdown, reinstall video card, reboot, all is well.  Reinstalled viddeo card drivers, it was recognized.  The system was stable for a couple of days (no heavy loads on vidoe card) then it happened again!

Questions:

Is a my video card overheating (I haven changed the defalut fan speed which is probably way too low)?  It works sometimes, can VC failures come and go or are they usually either alive or dead?

Can this be a memory, either system or video, failure?

Can this be corrupted BIOS (I did flash the BIOS with Dell recommended software during one of my previous troubleshooting attempts: It flashed the same version already running)?

Whats with the numbers and slashes throughout the startup and operation?  Hardware failure (video or otherwise) of some sort??  I'm at my wits end, this has been going on for 2 weeks and the inconsistency of it all is frustrating!  Thanks for any help!!