|Can you right-click, say a text file, and see the Open button? Is the Open With button bold? The bold option is the default option when you double-click the file, folder, shortcut, etc.|
This doesn't yet sound like a problem that would warrant a re-installation of your operating system. I try to use that as a last resort in most circumstances anyway. If you were to re-install Windows, you'd insert the CD then reboot your computer. If the BIOS is not set to first try booting from the CD/DVD drive, you'd need to adjust the boot order in the BIOS to put the CD/DVD drive before the hard disk drive.
Apologies if I don't respond to your reply immediately. I don't check this site daily, but you're welcome to PM me as a reminder.