Ok heres my problem. For the past few weeks My computer Has been shutting down on its own, the thing is sometimes it restarts right away and other times it could be an hour or two It will just boot back up on its own. I have tried everything I could think of I swapped the power supply with another one I had and same problem, Took my video card out and tired another still same problem. My processor rarely ever runs hotter than 35c
I get no errors from windows. I reformatted my windows still same problem. I tried different ram still same problem. When my computer works like it is right now It runs perfect, the thing is It could shut down any second, or it could shut down two hours from now. Any help would be great I'm totally stumped.

Your hardware list would provide some light. Sounds to me like hardware/driver issue.

If you want stability, you should increase RAM voltage. Some RAM (like GAIL) are power-hungry, and default voltage just isn't enough.

Couple of Q's:

Are there any errors logged in event viewer?

How high is your VGA temp?

Are all of your motherboard drivers installed?

Do you have any "unknown devices" or problematic devices in your device manager?

Did you try setting RAM timings manually?

Have you OCed your CPU?

Thanks for the reply I have a MSI K7N2GM-L Motherboard with 512 333mhz ram ,amd 2500 barton. msi geforce 6800 gt oc,win xp sp2 fully updated,now for the questions

1. I have no errors in the event viewer and I get no blue screen errors, I set windows to not restart on system failure and still no errors

2. I have never seen my video card temp over 62c and it says slowdown threshold 120c

3. yes all motherborad drivers are installed , i just reformated to try to fix this problem

4. no problems in device manager

5. no I have not changed any ram timings, never had to before

6 never oc'ed processor

try using other processor see if it works..

I would try, But I don't have another processor.

After wrapping my head around your problem I could think of several reasons why your machine shuts down on it's own:

- PSU - possibly the other PSU you tried does not produce enough juice to run your machine or it has similar power outlet problem like your original one. Bare in mind that PSU's power outlet decreases over age. If both are similar age and wattage, chances are that they will both have same "aging" problems.

- the silliest reason (and, somehow most likely) is the power cable of your machine, or the socket it is plugged in. Loose connection can cause mobo/CPU dying symptom, without any error reports/BSODs whatsoever.
Simply change the socket and/or the power cable to see if that's the case.

- motherboard or CPU failure - this is worst case scenario. No real way to eliminate one or the other unless you have spare CPU (which you don't), or spare mobo (yeah, right, you sure have extra one of those lying around)

- incompatible PCI card - I had a PCI modem that would cause shutdown every time I try to dial. Maybe you have some old or no-name PCI audio card with outdated drivers?

- weird RAM issues. I experienced similar behavior of my machine back when I was experimenting with overclocking. That would happen usually when I go overboard with MHzs. Countermeasure is to increase the RAM voltage, or to under-clock the RAM itself.
What you're experiencing can be caused by RAM-motherboard incompatibility. That would be so if you haven't consulted your motherboard manual when you were purchasing the RAM. I did the same mistake and spent almost a year trying to figure out the right timings. That's what happens when you ignore the list of supported RAM models/manufacturers/configurations. I said "weird RAM issues" because one would expect memory access errors appearing in pop-up windows every now and then, but with memory sticks one can't ever be 100% certain.
Given that you have 1/2 a Gig of RAM, I take that it is one stick, all you can do with it is to change the slot.

Does it do it with the hard drive out of line?