Could be a number of things including the recovery software on the hard drive partition has somehow got corrupted or could possibly be a hard drive failure issue
If you have a set of recovery discs for your laptop I would suggest using these to reinstall the operating sytsem
Do a full clean reinstall using the discs
If not then you may have to bite the bullet and purchase a set from Sony
Or if you have a retail copy of Win7 you could do a clean install of that but you will have to reinstall a whole load of drivers and some of your functions may not work ie bluray player without the original software
You could remove the hard drive and get it tested separately if you know someone that can do a diagnostic check on it for you
Keep us informed on how you get on