maybe its some background services .open up task manager and see whats eating the cpu .How do say it is "always at 100%"
as the pc will auto reboot is the cpu is stressed soo much or might hang.DID it happen before u clean??(like more than 75 percent cpu usage when left idle)
Update:
My computer starts with the normal cpu usage which is around 20%, and I can easily use 1 page on google chrome, but when I start to use 2 different pages at the same time (youtube and facebook in my case) or open a program such as steam, the usage will instantly raise to about 100%. http://imgur.com/8LHz37A,99X04mU#0