Help to restore my PC

My son took total control of my PC during the holidays. Now he is back at the university, but to my surprise he has changed the OS to vista ultimate from the home premium version. I have lost most of the functions and programs which came with the computer. Fortunately the original disk image is in a partition on the hard disk. I have tried F11 on boot up in order to access system recovery but it does not work, because the recovery program seems to have vanished from the PC.
My PC is HP Pavillion S3230UK
Current OS Vista Ultimate.

I need to restore it to the original state. Please help!