Question : Problem: System monitor shuts off.  Computer still runs fine.  Please help!

Here are the machine specs:
Supermicro P4DCE+
Dual 2.4 Ghz XEON cpus
1.5 GB RDRam
256 mb Nvidia Graphics Card
80 GB SATA HD
CD-rw
3 case fans, 2 cpu fans, 1 PS fan, 1 Ram fan, 1 Graphics fan = 8 fans total
Win Xp Pro SP2
AutoCad 2006

You might have figured out where I am going with this thread after I listed all the fans I have.  Well I think I have an overheating issue but I can't find it for the life of me.

How it displays itself is after a while I get multicolored lines all over for the screen and then after about 2 or 3 seconds the monitor goes black.  The computer does not shut off just the monitor.  The light on the monitor turns yellow like it does when it doesn't receive a signal from the video card.  However the computer is still running ( I know this because today I had the internet radio playing and it continued to play even after the monitor shut off).

Day one:
The first thing I did was open the case and use my desk fan to help cool everything.  I initially thought the video card was going bad so I purchased another one.  The problem continued.  

Day two:
My next thought was either the ram or the cpus.  I didn't have any extra ram so I removed one of the cpus and ran it that way.  Well after a couple of hours the machine messed up again so I swapped the cpus and ran the rest of the day with no problems ( I still had my desk blowing into the open case).

Day three:
The computer ran all day and nothing happened (although I did turn the computer off during lunch).  Still had the desk fan blowing into the open case.

Weekened:
Didn't run the computer.  Did research at home.  Read where to tell computer not to reboot on error.

Day four:
After 2 hours the computer messed up again and gave me a blue screen with this info:
Driver_IRQL_NOT_LESS_OR_EQUAL
STOP: 0X000000D1 (0X00004497, 0X00000007, 0X00000000, 0XB98B180B)
NV4_mini.sys Address B98B180B base at B96FE000, Date stamp 4269449f

This sounds like a video driver issue but the computer has messed up again and I have never gotten another blue screen, just the multicolored lines all over the screen.

I remembered I had an extra memmory fan so I installed it.

Day five:
The computer ran for 8 hours today before I got the multicolored lines.  I removed the desk fan after I installed the memmory fan.

I am at a loss for what to do next.  Can someone please point me in the right direction?  Offer some good information?

Thank You,
Will

Answer : Problem: System monitor shuts off.  Computer still runs fine.  Please help!

so your system is slightly underpowered. You see the results : sometimes it works, sometimes not.
Frankly, i would put in a 450 or 500W PS, and get rid of the fans (it may still run ok on this PS without the fans)