I ran hard drive tune.
Error Scan (tab) came back perfect but the Health (tab) came back with this error;
(C7) Interface CRC Error Count 99 99 9 11 - attention
Description: Number of interface communication errors 11
Status: There were communication errors. This may be caused by a damaged cable.
Is it possible that the randomly resetting or when running a browser for a long time or copying a large file from one drive to another etc etc is because of a bad HDD / SATA cable ?
If you have another cable around it would be worth a shot to try it, even if you took the one from your cd drive.