|The very first step would be to check for viruses.|
Firstly download, install and run MalwareBytes free version:
After that download and "Save" this ADWCleaner file from the blue download button near the top of the page:
Go to the saved file and double click it to run the Scan (there is no install). There are options but it is usually safe to then run the Clean.
Both of these often unearth and fix what your Antivirus can miss. If either of them find anything then copy/paste their logs on here as separate posts because your computer might need further attention.
I will not be available for a week but hopefully someone else will continue this thread.
Always pop back and let us know the outcome - thanks