I am using AVG anti-virus software..and the best thing is that its free. Download from its website and scanned for virus.
In addition, download ad-aware to scan for spyware as welll. Both softwares are free and work reasonable well.
If there are no virus, it could be hardware problem or maybe the OS problem. reinstall your OS and if it still does not work..check the temperature of the PC or change power supply.
