So the PC shows some life but won’t start Windows. Try again but keep tapping the f8 key after the brief flash of activity you get when you first switch on. You should end up in “Safe Mode”, from which you can restart and maybe that will fix it, if not, you are going to need help.
It could be anything from damage caused by a virus, or hard disk failure. It may not be expensive to fix and you may not have lost your files, but you’ll need help.