Looking to safely clean my Windows Xp Sp2 registry of un-needed cluter that may be slowing down my computer.

my computer keeps rebooting on start up!! before windows loads!! win i use the function key it still restarts!! no matter what i choose to start in!! so i have read in many instances that i need to reinstall!! so the question is if i download windows xp pro to my hard drive!! can i run the installer from dos mode??

I’ve tried several registry cleaners that have scanned my Windows XP but didn’t fix more errors than 15. The last time my computer was scanned, over 600 problems were found in my computer’s registry. Does anyone know of a registry cleaner that is completely free and can fix all the registry problems without buying the un-free version?

the registry cleaner must be compatible with Windows XP Home Version.

I have Easy Cleaner 2.0 on my Windows XP PC. Upon running the Registry cleaner, it came up with 220 invalid entries. Is it safe to delete these? Should I somehow backup my system before I delete them?