If you have the Windows licence key (sticker on pc) then all you need to do is borrow someone elses installation disc. Providing they are excactly the same version, you should be able to do a full reinstall of Windows. This is not illegal as you pay for the licence key. You will lose everything though so this is a last resort. If the hard drive has failed, you can get a replacement 500gb mechanical drive for £25 or a 120gb solid state drive for about £50. You can also get a 'caddy' and might be able to recover files off the failed drive. Search on the net for all these terms if unsure. No room here!