|Very odd issues. Start with event logs. |
Might also unplug network cable just to be sure someone hasn't hijacked your system.
Might have to sweep for spyware and adware and virus's.
Boot to a live cd and see if it works OK. Might help tell hardware from software.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10