Also consider the possibilty of other programs causing conflict, where it didn't before.
Use msconfig to disable all the programs loaded at startup. then reboot and put the tick back in the box for each one, reboot after each one. If there is a conflict you will find out when you have just added it back, if that happens, disable that one again and continue until you finish the list.
Don't worry for now what you disable, if a program really needs something running, either that program\function just plain wont work, or you'll get an error message.
There are ways to get things to work together, but just try to fix the booting problem first.