then several chkdsk scans run on it - some of which worked perfectly some caused the machine to reboot.
-nudone
Ah ... that looks strange. Why should chkdsk cause your system to spontaneously reboot EVER?
Sounds more and more to me like a memory issue or a heat/power issue.
Run MEMTEST+ as we suggested tonight but also check temperatures and also check the recommended PSU capacity for all the hardware you have. I was surprised to find a system I recently built for a friend had a mobo manufacturer's recommendation of a minimum of 450W, 600W for dual crossfire video cards and even higher for lots of memory.
All these manufacturers keep wittering on about low power consumption and cool running systems - strikes me that most systems are running a lot hotter these days and consume almost 4x the power systems did 5 years ago. I still have a Pentium III / 1Gb system that runs on a 160W PSU and doesn't need any case fans to run stable.