Whenever you install new EPs, believe it or not they do put more demand on your computer's system resources graphics and performance wise. Have you tried updating your video card drivers? The red flashing walls is something that's typically common to that type of need.
(What type of video card do you have by the way? You can always find out that info by typing in
dxdiag in your "Run" command box in the Start menu. Then when the DirectX Diagnostics Tool pops up, click on the "Display" tab and the info on your card will show up in the upper left-hand box. I can tell your right of the bat, if your graphics card is anything with the name "VIA/SG3 UniChrome IGP", your video card was never destined to handle anything graphically sound beyond the base game... because my old PC has that card, and all of the red flashing began with the water in OFB. :lol:)
