Hmm, maybe try backing off the overclock a wee bit, RC5 is not the most demanding program on your CPU but it does work the MMX cores quite hard. Report back, this should be interesting. I am running the Dnet client and SETI on a dual-celeron system and it's been running nonstop under Win2kPro for... 4 weeks, 7 minutes. I have had TaskManager open for the last couple days, too.