T5500 Locking Up

I have a Precision T5500 that is locking up every few days. It runs Win XP SP3. During these lockups the screen freezes (clock indicates time of lockup) and the mouse and keyboard are unresponsive. The only thing left to do is a hard power down. Once the system is restarted, it runs as normal for 2-4 days, then another lockup. The Intel RAID software does a check on the drives at restart. There is no info to go on in Windows Event Viewer. I've done a *.log search in explorer and opened every recent log and there is no info to go on there either. My gut feeling is that it's hardware, but I don't have any data to go on. Upon restart the chipset fans come on, haven't observed them in lockup condition. This PC is not connected to the internet. Any help is appreciated.