Try this:
Put in the windows cd and boot from it.
See if you can delete/create/format through the setup.
Do not ofcourse delete C (unless you want to do a fresh installation of XP)
If you want to do a fresh installation:
- Partition/format as you wish
- Install XP
- Install system drivers (check device manager and make sure there are no more exclamation marks or red crosses)
- Install the drivers for your devices (printer, monitor, keyboard, scanner etc)
- Install avast
Do all the above before(!) going online.
- Install the applications you are normally using. (text editor, music application or whatever it is you want to use)
- Configure everything to your needs/wishes
- Create a drive image (very handy if you need to reinstall again and much faster then a fresh installation)