Glad to hear from you.
I would like to confirm if you ran Hardware Diagnostics on your computer. If yes, did u get any error code?
If Hardware Diagnostics pass, then I would suggest reinstalling windows on your computer. If you haven’t received any Operating System discs with your computer, your computer manufacturer should be able to provide you the copy of that.
I am not sure if the copy of that disc on Ebay would work or not. But I would suggest you to get the Discs from your computer manufacturer which should be provided to you free of cost.
Else, you can even reformat your computer using recovery partition. For steps you can refer to the URL mentioned: http://www.ehow.com/how_8464910_ref...
Thanks & Regards