Safe Mode
This gives you access to a VGA driver.
If the above doesn't help.
Use Safe Mode with Networking if you need internet access.
Click Start - All Programs - Accessories - Run and type
msconfig
Then go to the Boot tab and click Safe Boot (also tick Network if needed). Reboot. Come back here and untick Safe Boot to return to normal mode.
or
If your computer has a single operating system installed, repeatedly press the F8 key as your computer restarts. You need to press F8 before the Windows logo appears. If the Windows logo appears, you will need to try again. [From Start - Help and Support]
Startup Repair
This also can give you a command prompt.
If your computer has a single operating system installed, repeatedly press the F8 key as your computer restarts. You need to press F8 before the Windows logo appears. If the Windows logo appears, you will need to try again. [From Start - Help and Support].
On the Advanced Boot Options screen, use the arrow keys to highlight Repair your computer, and then press ENTER.
Select Startup Repair.
Startup repair makes a log file. See C:\Windows\System32\LogFiles\Srt\SrtTrail.txt
.
To access if Windows won't start, on the Advanced Boot Options screen, use the arrow keys to highlight Repair your computer, and then press ENTER.
Select Command Prompt. (this is where you can undo anything)
Type
type C:\Windows\System32\LogFiles\Srt\SrtTrail.txt |more