I've had this problem, too, but I just learned to login as root, and type in kdm. If it is setup for multiuser, then it'll let you login normally.

Also, putting XDM ahead of KDM using Sys-V can help, as well as multiple KDMs. MAKE SURE IT IS IN THE RUNLEVEL THAT KDM IS ALREADY IN!!!

And, like Mr Ed said, don't let it lose power.