I had problems with my SN45G
It kept freezing after 20-30 minutes or so of being on, no matter what it was doing.
Each time it would need restarting, and on restart lost the BIOS settings every time i.e. back to December 2003 00:00:00, 600MHz etc (XP-M 2500+).
I reseated the Heatpipe, upped ram timings, underclocked, all to no avail...
Then, I removed the battery and replaced it with that of my old PC - it's working like a dream. I've got my Twinmos PC2700CAS2 running at 208Mhz 2.5-3-3-11 with no errors on memtest86!
If all else has failed, try the battery, even just reseating the existing battery. You never know...