Well it seems you may have overheated the gpu or cpu if not both hard to say sounds like it need a good clean out buy sum compressed air from Dicksmiths or sumthing check all the vents and fan, no good being clogged with dust. if you end up takeing apart apply artic 5 thermal paste to cpu this is what i did seemed to help with heat. Also the toshiba hard drive emmits mega heat a upgrade of a good harddrive will also help.
You also could be infected which would make your problem worse. What antivirus, malware, spyware apps you using. Malwarebytes & superantispyware are good scanners.