Crashed.

A friend left her pc on,went out for the day,and didn’t came back ’till late to find her pc just crashed by iteself!

She tried to follow instructions on how to reboot it,but the instructions doesn’t work for her!She read on her pc that there’s something wrong with the hard drive such as SAT and DATS (She can’t remember the last bit)? She’s wondring does she need to buy a new tower, because she can’t even reboot it! Or does she have to take it to PC World for them to fix it?