1/It maybe due to a new driver or program you installed so try and do a restore point.
2/ Try pressing F8 and load in safe mode and see if it freezes.
3/ Look in "event viewer for any errors and follow the links to help and support online.
4/ It maybe hardware/driver problems so try removing non essential hardware and replace one at a time to find out which is causing the problem- you may end up having to reactivate with Micr$oft so do this last.
5/ try entering the bios (press DEL at bootup - just exit without making changes and see if it loads OK - if it does you may have to reinstall motherboard drivers - also get updates for your bios and motherboard.
6/ Also when you first boot (at the same time as you would press DEL to enter the bios) press the PAUSE button and wait 30 seconds - then press any key to continue - if it starts OK let me know.
7/ Goto this site and see if you are overloading your power supply http://www.jscustompcs.com/power_supply/
If I think of anymore things you can do I will let you know.
lately when I boot up, the screen remains blank so I turn off using switch on processor as I cannot use start/off.
It usually boots up ok this time but I ask why this should happen.
I have a good clean/maintainance routine and I try daily to use
clear all my inbox/sent items/deleted items/rec bin
Imy o/s is XP home