I don't think the magnets are to blame.
Turn off Aotomatic Reboot on System Failure.
That way you will get an error screen instead of a reboot which tells you nothing.
Check your Event Viewer for error warnings.
What realtime protection are you using, Firewall, Antivirus, Anti Spyware/Malware?
Are you confident of your electricity supply?
Save yourself getting hit with a lot of questions...
Download, unzip, install and run Everest Home Edition
http://www.comcen.com.au/~fed/everest.zipSelect
Computer>Summary from the left hand screen.
Right click in the right hand screen & select
Copy AllPaste the details in here.
[highlight]Edit:[/highlight] You could also download a program to test your HDD, if it is a magnetic problem then your HDD is the thing that would be effected.