Can you start it in safe mode? ... to get there try this -
1) When you swtich on keep pressing the [f8] key. It will bring up the Advanced login menu.
2) Using the arrow keys select "Safe Mode" and hit enter. Lots of writing will scroll up the screen and eventually Safe mode will open.
1) When you boot to the login screen, hold down the SHIFT key and click on Restart. This will take you to the troubleshooting option screen where you can enable Safe Mode.
2) Click on the Troubleshoot button.
3) Select Advanced Options.
4) Now choose the Windows Startup Settings option.
5) Finally hit the Restart button.
This should let you into the Advanced Boot Options screen. Choose Safe Mode (using the arrow keys) and hit the Enter Key. When it eventually opens dont worry if the icons look big and the screen shows wierd colours - it may be using different graphice settings in Safe Mode.
Now do a full antivirus scan and then reboot your PC.
Let me know how you get on.
I really appreciate kudos points as a payment for solving issues :o)