Have you tried using System Restore from a command prompt
in "SAFE MODE
The symptoms you describe could be malware related or they could be due to hardware or overheating problems caused by a failed processor fan, bad memory (RAM), failing power supply, underpowered power supply, CPU overheating, motherboard, video card, drivers, dirty hardware, etc. If the computer is overheating, it usually begins to restart on a more regular basis. If your not finding any malware then its sounds like the latter problem. When was the last time you cleaned the inside of your computer?
Dust restricts the airflow and prevents proper cooling. This in turn can cause overheating and faulty processor fans which can result in unexpected shutdowns, random restarts, booting problems, etc.
- Open your machine, check all the connections and make sure the fans are all operational.
- Check the heat sink on the processor to ensure it is not blocked with dust or debris.
- Remove the CPU's cooling unit and clean the fins on the heat sink that sits under the CPU with a can of compressed air.
- Inspect the thermal compound between the CPU and heatsink as it can break down over time so.
- Remove the cards and RAM modules, clean the contacts and reseat them.
- Feel the CPU heatsink when it powers down. It should be warm to very warm but not hot.
See "Cleaning the Interior of your PC
" and the "Illustrated How to Replace an AGP Video Card
" (use as a guide to clean & reseat).
A word of caution about WinCleaner. This software also includes a registry fix/cleaner. Using these types of utilities improperly or making incorrect changes to the registry could adversely affect your computer and render it inoperable. Did you use that feature and if so, did you backup the registry before making the changes.