Okay well my pc is having problems(details below) & i got some recomendations to do a registry clean. I have ccleaner, & i dont know if i should delete what it detects under the registry clean? Should I? Will anything bad happen to my pc? Thanks

Pc Details-
Okay, I close everything down, and then I go to Start, & click shut down, then that little window appears with the options of turn off, restart, & stand by. So I click Turn off, & once i do that, it goes to the shutting down screen-"Windows is logging off…"-like that. But then 5 second later, instead of turning off, it goes back to my desktop. Then I wait 15 more seconds & A "End Program Now" window appears with the progress bars for 1.5 seconds then dissapears. & then after all that my pc just freezes, everything is frozen, even ctrl alt dlte. Does Someone know what to Do?? Is it a registry problem? Should I try ccleaner, what?? I have to hold down the power button in the end to turn it off. So Any one???? –I Have Windows Xp Home