Run memtest overnight

First run Memtest86+ on the machine overnight, to test that the CPU and memory are error-free. Also run a CPU stress test for 5 to 10 minutes to check CPU is reliable and adequately cooled. The easiest way to download and run these memory and CPU testing tools is with the Ultimate Boot CD.

Also use System Rescue CD to check bad blocks on the hard drive, before trusting it with any data: badblocks -v -s -w -c 4096 /dev/sda
If the machine does not pass memtest and CPU stress and HDD tests without any errors or warnings at all, then do NOT proceed any further until this is rectified.