If you are able to access the internet on the computer I would highly suggest running this free online antivirus scan from a trusted antivirus company:
http://housecall.trendmicro.com/If you are infected with a virus or malware this product should detect and suggest solutions. Secondly are you able to start the Windows firewall service manually after a restart? To attempt to start the service manually right mouse click "Computer" then select Manage and expand the Services and Applications, select services and find the Windows Firewall serivce and check the status. If it is not running right mouse click the service and attempt to start it.
