Helly terry, welcome to Sevenforums
Instead of trying to purchase a new OS, you might try to use the restore CD first: System Recovery Options
If you choose to attempt to keep the OS going and fix it instead: The following paragraph describes how you may need to uninstall some programs. I recommend using Revo Uninstaller Free to remove the programs as it does a better job than the Windows Uninstaller.
I would recommend uninstalling everything
(Or as much as you can - the more the better. Do not uninstall any drivers
or updates listed in the control panel or Revo Uninstaller, however), and running this tutorial
). If you use Revo, select a program to uninstall, click uninstall, make sure you choose "advanced" mode when prompted, and when the options arise to delete extra registry items or files, make sure you click all of the individual items and files and select 'delete', then next. After you've followed all of these steps, download Ccleaner
and do a registry scan and delete anyything that presents itself as needing fixing.
The reason I would have you uninstall as much as you can is if you are going to wipe the system anyway, you might as well. And this way, it ensures the problem doesn't lie with a program, and allows your system to more easly get fixed. If Control panel has more programs listed (not drivers or updates) that aren't listed in Revo, uninstall them in the control panel.
If ever you have any questions, don't hesitate to ask them. If you have any trouble downloading the software I've recommended, let me know, and using any kind of virus scanner you may have, try to detect if your system has a virus. If you do not have a functioning scanner/antivirus, let me know that also.