So-called antivirus

Hello Everyone
I have a problem similar to alot of posts dealing with the system restore. Also my C drive doesnt show up on my device manager and a whole host of other odd symptoms that I cant think of offhand.
It started with a system scan done by some sort of antivirus that I dont even remember downloading. It said I had a bunch of viruses and etc and needed to purchase to fix the pblms. I didnt purchase and it has led to these problems. I have tried a bunch of different things that have seemed to slow down the problems but not completely fix whatever is wrong. I have given up on trying to fix it myself since i really dont know what i am doing and my "IT" department has no clue and no motivation to look further into it. They just want me to use a different computer (easy fix for them and days of downloading programs and files and etc. to make the new computer able to do what my computer now can do). I would really appreciate help on this one. Let me know if you need me to run something and send an output file or whatever else may be needed to diagnose/fix this problem. Thanks in advance.