It could be a video card problem (I suppose). If that’s the case, changing out the video may solve your issues in the short term.
A five-minute start-up time is something we see with systems with several hundreds of extensions. Can you tell us a little bit more about the details of your server and what your ‘base’ configuration is (installation parameters, etc.)
One thing I will say is that a 4G motherboard is the base minimum anymore. SNG7 (IIRC) requires something like 8G to operate without swapping its brains out.