1. Which graphic card did you have before?
2. Which card have you replaced it with?
3. Did you uninstall your old drivers and revert to a default MS graphics driver after removing your old card?
4. Which version of Windows are you using?
5. Do you know the make and model of your motherboard?
6. As far as you can tell, is Windows starting normally (normal hard drive activity, etc)?
If you can provide as much detail as possible to each of these questions, I'm sure we can get you sorted :)