Hello ubuntuuser, welcome to Seven Forums! That's an appropriate handle.
You may need to start over, here's some interesting info you may find useful and be sure to post back with any further questions you may have and to keep us informed.
After you have copied out
or made back-ups
of the data you need to save to external media; if you can find an exact Windows version that the PC shipped with you can do a clean install
using the activation key on the COA sticker attached to the PC though it may require a robo-call to MS to sort the OEM batch-key.
How to Activate Windows 7 by Phone
If you can't find an exact same version, you could use the info in this tutorial to create an "all Versions" installer of any version Windows installer, to install using the same method I posted above.
Windows 7 Universal Installation Disc - Create
After you have made backups of everything you care to save, the best method is to do a complete wipe (secure erase) of the entire Hard Disk Drive first, it over-writes everything, all the old Windows code including all the old drivers/programs, giving you the best possible space to install Windows to.
SSD / HDD : Optimize for Windows Reinstallation