Error: Sfc Database, Troubleshooter, Sdiageng.dll

I am having issues on an HP windows 7 home desktop. it had been infected by a virus, but this error came before it. Anytime I try to run Microsoft's fixit or any troubleshooter, it comes up with the error of that Sdiageng.dll is either missing or corrupted. so, I tried to run sfc from command prompt. well, if finds stuff alright, but alas, it can't fix it! so I look at the log, and it says that it's database is also corrupted. well, I have no idea what to do. I found sdiageng.dll in the windows directory/system files. it's there. I even replaced it. still, same error. this all started with me trying to fix windows update error 1 and 643. I have run numerous scans of malwarebyte's and trend micro and super-anti-spyware. they found some stuff, I got rid of it. but still the error remains. I have searched around for a way to be able to fix sfc's database, I tried one, but the commands were for vista. I was hoping it'd work, since vista and 7 are really similar, but it didn't. so I am hoping someone on these forums can give me some help. I know a fair amount of knowledge of computers, and whatever I don't know, I can usually find on google. and I know some information about malware and viruses and the whatnot that's bad stuff. I've had to remove malware twice from computers and I didn't kill them in the process.