I bought an older Pentium 4 PC to run Linux and use as a server/music player/etc. I installed Ubuntu, and basically everything works as expected software wise.
However it often freezes completly some time after booting. The screen just stays as it is, with no interaction possible anymore except for hard reset. No SSH over network either. This happens within 10 minutes after booting usually. If it does not happen after that time (usually after I already rebooted it 1-3 times), it runs fine for hours. Almost like it needs to warm up or something. Another hint: 2 times it actually froze in the BIOS screen right after turning it on.
What could be the cause of this? I checke the RAM already with MemTest, but it came up ok.