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It is not a good idea to use any account with Administrator rights to do everyday computer surfing. Admin accounts should be used only for installation or deletion of programs, and for anti-virus and anti-spyware scans.
In your case, try using 'System Restore' in Programs ---> Accessories ---> System Tools, and restore the computer to a previous known good date.
The re-start in 'Safe Mode' and run anti malware programs.