In reply to mypyrex:
You will (almost certainly) need to erase the hard drive and start again from scratch. This means you will have to reinstall:
Drivers (though windows 7 is pretty good at doing this itself)
Programs
Your Data
When I have done this before I've done it the hard way which is back up everything, do a search-and-destroy through settings to find out the exact model of my hardware and then get the win7 drivers for it, and wipe and restart.
There may, however be whizzy ways of doing this via the cloud or utilities these days which I don't know about.