I was messing with the cmos and tried to overclock my pc. Well that didn't work so I lowered the speed back to what it was originally was and went to bed. Woke up the next morning and was unable to get past the Windows Xp welcome screen. It seems to load up fine but it gets to welcome, but wont show the login screen. It just sits there saying welcome. I'm not sure why changing the cpu and bus speed would mess up the OS. HELP

go back into the bios and set the defaults and save changes and exit the bios

I have changed everything back to what they were yet I still just get that blue windows xp screen, but it does not give my the chance to log in.

Your CMOS may be corrupt. Go into the BIOS setup screen and copy down all the settings as you want them. with the power off, open the unit and move the CMOS erase jumper to the clear position for however long the instruction book say to leave it there. Move the jumper back to the normal position and turn the unit on. The PC should report something like CMOS error -- defaults loaded and the real-time clock will be reset. Go into the BIOS setup and re-enter your desired values. Let us know what happens.