Glad that helped. GFX drivers are a bit temperamental. I've probably changed something that your driver/system combo doesn't agree with. The crazy thing is it'll probably go back to normal after your next GFX driver update.
That sounds like a driver issue. Make sure your GFX drivers are up to date, but if that doesn't help you can switch to D3D. To do this add 'D3D7' or 'D3D9' to the command line. In Steam right click HSL in your library and select 'launch options' to add command line parameters.
I saw that HSL had patched, started it up to see what's what and found that I can no longer play in full screen mode. HSL is fine in a window but in full screen the play field doesn't update as in it's a static picture.