PC Keeps rebooting

Reference: http://www.d-a-l.com/help/archive/index.php/t-1484.html
Support line to check hard drive: http://support.wdc.com/download/index.asp
Other References: http://www.pctechforums.com/modules.php?name=News&file=article&sid=391
http://www.windowsbbs.com/showthread.php?t=50640