Man, your going to have to be a lot more specific, give every little detail you can...

What are the specs of the new PSU you installed? How old is it? Why did you change the CD drive?

I'm assuming most of the problems you were experiencing before were resolved once you changed the PSU?

But on occasion you still experience random reboots and freezes at the mobo splash screen?

Well, you could try resetting the cmos just for the heck of it, but I doubt that will solve anything.

If my assumptions are correct, then something is telling me that since your PSU was faulty (we know this since most of your problems went away when you replaced it), your mobo might be on it's way out as well... When PSU's go bad they like to take things with it...