My PC experiences periodic interference (distortion of vibrating lines) & becomes unreadable how do I block?

Help! my computer has been taken over by a cyber gremlin (for lack of a better word). The interference occurs even when not connected to internet and then mysteriously they disappear (my experiment of shouting the most loathsome explicative appears to have little impact except on my elderly neighbor). This malady has festered despite my paying big bucks to have PC scrubbed, and allegedly professional installation of multiple software programs including: firewall, anti-virus, mal-ware, anti-spam, and spy sweeper. What is this – how do I block? Is there a cyber-god that I need to make an offering as I’ll gladly enflame a floppy disc as a sacrifice to appease this contemptible fiend.