Could be overheating, try hoovering the vents.
Download AVG free or AVAST antivirus and run a scan (both freeware)
Also maybe Spybot Search and Destroy or Antimalwarebytes for the spyware/malware (again both free). Uninstall the norton first btw.
Could also be failing ram. if you got more than 1 stick, take one out and try it, then the other to see if you got a bad stick.
Good luck
Download AVG free or AVAST antivirus and run a scan (both freeware)
Also maybe Spybot Search and Destroy or Antimalwarebytes for the spyware/malware (again both free). Uninstall the norton first btw.
Could also be failing ram. if you got more than 1 stick, take one out and try it, then the other to see if you got a bad stick.
Good luck