Start with
this guide and follow the instructions to the letter.
If you fail to solve the issue running the software in sequence and according to the detailed instructions (including how to get around the virus blocking certain removal programs) then follow the instructions for seeking help. The site has a number of trained volunteers who will help you resove the problem.
In my (considerable) experience running the software suggested, in the way suggested and in the sequence suggested has always solved the problem I have been dealing with.
It is all free.