In need of advice!

Hi there, I have windows vista on my hp pavilion computer. A few weeks ago, i started experiencing problems so i ran virus checks and registry scans etc. The virus' have been cleared but my computer is left in a state.
e.g. when i click to open a program or click to hear music, a box comes up saying; "Choose a program to open with", and another case is in the control panel, some of the items in the control panel do not open at all ".....Cannot be found". In both cases i see the file; 'Rundll32.exe'. Is there a problem with it thats causing this?

Yesterday, my cursor on the screen stopped moving, i used 4 different mouses, but the problem is still the same, now i have to use the keyboard to get anywhere.

How do i fix this? My idea was to some how put everything on to a new drive (i have very important files on there) and then reset vista to factory settings? Is this needed? or is there a way to do it without loosing my files and programs.

Many Thanks!