Turn off the computer. Start computer, press F8 to get menu, access SAFE MODE. If you can get into SAFE mode you can select to restore to a previous restore point. If that still doesn't work, insert your Windows DVD and select from BIOS to BOOT from the DVD, then select Windows REPAIR. If that still doesn't work, then your Windows is fud up or the Hard Drive is. Download DBAN, wipe the HDD and reinstall Windows, Drivers, then programs. If you have any errors while DBAN or Windows install then the HDD is going.