Hi
Ok when the machine starts keep tapping F8 till the Advanced boot options window appears
Using the arrow keys move down to safe mode with command prompt and hit enter
Next once the command prompt has loaded type sfc /scannow and hit enter
NB between sfc and / is a space
let the scan run and if any problems are found then windows will repair them.
If this does not work then using the tapping F8 at start up again try to use system restore to roll back to a time that your Pc last worked . To do this from within safe mode with command prompt type rstrui.exe and hit enter and choose a date in time when your machine last worked fine .
Post me your findings
Checkurtech