I just built a new system with the following specs:

MSI p7n-sli platinum motherboard, Intel 8400 wolfdale processor, 2gb Gskill DDR2 pc6400 memory, and a Geforce 8800GT video card. I used my old WD 250gb hard drive in this system after reformatting it. I installed Windows XP professional as my OS.

Them computer runs very fast and cool when it is running. However, at random times (mostly when applying a patch or copying large files) it toally freezes up. The cursor is frozen on the screen and no keyboard commands whatsoever will work. If i press the restart button, it only hangs on the post screen. Then only thing that resolves this issue is to shut the system down and then turn it on. Upon rebooting, the computer runs perfectly again until another lockup.

Sometimes it will go a day or two without this happening. Sometimes it will happen 2 or 3 times a day. It seems to only do this when it is patching, loading a program, or copying files. Please let me know any diagnostics I can run to locate the culprit of this probelm. I dont want to let my time period expire to do an RMA if it is a faulty part. Thank you in advance!

In BIOS, bump the RAM voltage manually to 2.0-2.1v for PC6400. Also manually set the NB voltage to 1.45-1.49v. You may want to run memtest also and check for errors or faulty RAM. Memtest is on Ultimate Boot CD.

http://majorgeeks.com/Ultimate_Boot_CD_d4981.html

The problem seems to be your memory there matey just like badget has told you.
Try to do things here and there like badget had told you.
If the problem presists just tell us.

Thank you for your replies. I took your advice and increased the voltages on the NB and memory and I have, so far, not had any lockups. Hopefully this solved the problem. Thank you again for your help!

Just to remind you, don't increase your memory voltage too high or it will not last long. Adjust it to the default voltage as written on its manual.
Some work on 1.8-1.9 V, some works (like mine) 2.1V