|Ok, so basically you cannot boot into windows. There are a variety of options.|
1) Find out why the PC is not booting, and fix the problem in safe mode
2) Try and launch "Startup Repair" from the boot menu (Press F8 on bootup)
3) Try using windows recovery on the winows DVD. For this you require the media that came with your PC
4) Use any "HP recovery disks" you may have. I have never used them myself, but some other people have reported success using them
Good luck, and I hope that this has somehow helped!
P.S: Any chance you can post a specific boot error message that you may have been getting?