1-Put the windows 7 instalaltion disc in your optical drive and restart to boot from the DVD. You may have to change the boot settings in your BIOS if booting from a CD/DVD is not enabled.
2-On the Install Windows screen, make the appropriate selections for language, time, and keyboard, and then click Next. On the next screen, click “Repair Your Computer”. Do not click "Install now"
3-In “System Recovery Options”, select “Startup Repair”
4- check if your computer is working now.
If the problem still persists, restart your computer and choose safe mode, click start and type "system restore" in the search box on the Restore system files and settings window. Choose the restore point that you want to use. You should use the restore point with a date when you still don't have the problem you are facing now.
let me know if you are using another operating system (windows 8 or 10 for example)
Hope this fix the problem
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