From what you are saying it could be coming down to a priority issue.
Every program that runs on your computer has a system priority. Which basically means that windows is trying to figure out what program is most important and give that one the resources it needs to run. When you start the program manually, it gives it a higher priority than a screen saver gets by default. Screen savers are about the lowest on the totem pole that you can get as far as Windows is concerned, so if anything else, or everything else is running at the same time, windows will make the decision to give them priority of system ram, video memory, cpu cycles, or whatever they need.
Try this and see what you get:
Start the beta and then do a CTL+ALT+DEL to get to the task manager. Find MA3Beta under the process tab and then right click on it. Where you see it says "Priority" it probably says normal, because we found some problems already in this area, but go ahead and raise it higher and then see what you get...........
What you are doing here is telling windows that you want MA3 to be more important than other things, but keep in mind that if you leave it that way and you have MA3 running in a window while working with other apps you could be causing problems with them because windows won't allocate them what they need to run properly.
If that doesn't take care of it, then from your specs this is a notebook with a to go card in it. It could be coming down to a driver issue as well. I know in the past Dell requires specific drivers as they change theirs somewhat from standard drivers, or at least they used too I know with desktops, and I think with notebooks as well. Check Dell's site and see if there are any updated drivers for that card, and if there is any mention that you
must use their drivers only. If you don't then you can go to
here and see if nvidia's drivers will work better. Just remember to check with Dell's info first before trying nvidia.