Rogue disk defragmenter virus help!!!!?

Last night I was on my computer when avast popped up multiple times and said trojan alert, and malicious url blocked, then my desktop items started dissapearing soon they were all gone, and everything on my computer was gone. I rebooted mmy computer, and when i rebooted it this catalyst control center thing popped up, said my hard drive was messed, and i had a bunch of problems it couldnt fix, and I had to buy the advanced module. Ive had experience with securiy tool on a friends computer, so I rebooted in safe mode. the only way to the internet was through the safe mode online support, from there I downloaded malware bytes renamed it, and scanned finding fake trojan alerts pum hijack, which Ive never heard of, I quarantined those items, ran ccleaner, and security essentials, I believe it is all gone, but I cannot change my background it remains all black. any help please.