Few steps -
1) Start PC and right after the mother board screen is displayed keep pressing F8. This will definitely take you to safe mode. I assume you may have not tried this. if you already did, please forgive me for suggesting the same
Now i have a feeling the RAM could be an issue here. If you have multiple RAM's, just remove all, load a single RAM. Restart and see if this will load into windows.
where did u get windows 7? Do u have a CD? Need a little more information on how you loaded the windows 7 in the first place.
If you Used a OEM pack CD u can use that CD and press F12 in the boot screen to change the boot order and load from the CD drive.