Did you try F10?
Check and see if you can run the Sony Recovery option on bootup. It uses a hidden partition on your hard drive.How to Restore the Original Settings on a Computer Using the Hard Drive
I think you should be able to create a set of system CD/DVD restore disks while in Windows and then boot the laptop from the optical drive.
Otherwise I think this should help: How to Make a Windows Vista Repair Disk If You Don’t Have One