Software suddenly does not open

Hi, I have been using Corel PaintShop Pro for past few years, and suddenly it stopped working. I un-installed / re-installed and still no dice. I tried as a administrator and compadibility options...
I started using Microsoft Essentials Security recently - not sure if that would change things. I tried downloading a new patch from Corel, but it would not load - a pop up said it could not find the software on my pc - but it is listed in programs, etc and has 380MB listed as there. When I try to open - nothing happens. I also tried to open a jpeg with "open with"...and chose the program...still nothing. Any suggestions>? Thanks!

Hi
run a full anti virus scan
Download and run a full scan with malwarebytes.
If they are all negative, go back with system restore to a point a week before the problem.
http://www.vistax64.com/tutorials/76905-system-restore-how.html