might be - RAM is a common culprit for many problems with random restarts.

A lot of DDR1 motherboards seem to have speed Vs. RAM size allocation issues - my K8N Neo4-f (admittedly an s939 board) had issues with DDR400 over 1.5GB. Maybe yours is suffering from the same?

I'd also suggest considering loosening CAS latencies - 2.5 > 3, for example.