Mine kept doing that ages ago. Try the following: 1. As your computer is booting up (before it reaches the Windows loading screen), keep on pressing F8 until the Windows boot menu appears. Select "Start in Safe Mode" and press Enter.
2. Once Windows has loaded in Safe Mode, click on Start, go to Run, type msconfig into the box and press OK.
3. You should now see the System Configuration Utility. Now this bit calls for a bit of trial and error. We're assuming that the problem is caused by one of the Services or Startup processes listed under either the Services or Startup tabs in the System Configuration Utility window. So, what you should do first of all is disable both the Services and Startup and restart your computer (in normal mode... don't bother with the whole F8 thing this time). If it boots into Windows ok then we know that the problem is indeed being caused by one of the Startup processes or Services. Then enable all of the Services and none of the Startup and see if that will still boot. Then try vice versa. Keep note of what you've enabled and what will/won't work. You can carry on this process of elimination until you've worked out which Startup process or Service is causing the problem. Once you know which program is causing this problem, uninstall it.
If this method does not work, format your hard drive (back up your important data first, of course).
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