Random freeze

Hi guys, i asking this for my friend. My have have a lenovo U460 laptop. Using windows 7 enterprise 32bit(my sch installed for her). Her com will froze randomly without any specific action she need to do. The only way to resolve it is to restart but the problem still occurring randomly even after restart. Any idea why? Shouldn't be virus causing this as she just reformatted her com.

what is your sch ?

is it relevant to the subject?

well yes u install somethink then windows wont boot ?..when she formatted did she wipe her c drive also

Maybe hardware overheat or bad memory... can try diagnostic/monitoring software