It sounds like your issue deals more with anxiety than with the actual concepts - does that sound accurate? It may help you to know that you're not alone. Many people struggle with this kind of anxiety, especially under high-pressure, timed conditions (and that definitely describes the GMAT!).
What I would suggest for you is developing what Ron calls "openers" (and you may want to talk more about this with him, too). Essentially, how do you recognize, within 20 seconds or so, what the problem is testing and what kind of solution method you want to try? There are specific words you might see, specific formulas, even diagrams. Everything you see is a clue, right?
Turn this into a conscious translation, as though you're translating from one language into another. I see the words "integer" and "divisible by" so I know this is a number properties divisibility problem. I see that the problem asks about a general property that should apply to any qualified numbers, so this is a theory question and I could solve it by testing some qualified numbers. ("Qualified" means "fits the constraints given by the problem.")
Make it as specific as you can, to the point of noting (and translating) individual words. Tell yourself that you're just translating - you're not even trying to solve yet. You don't need to solve yet. You just need to translate it first. After you've translated, you'll have plenty of time to solve.
If you hit one that seems especially convoluted, and you're starting to feel panicky or especially blank when staring at it, make a guess, then do some deep breathing and roll your head around to loosen your muscles (you have time, since you just guessed quickly), tell the computer "Nice shot!" (pretend you're playing tennis and the computer just aced you), and then get ready for the next point (tennis again). (Note: if you're behind on time, drop the deep breathing and rolling your head around stages - just say nice shot and move on. Visualize playing tennis. You don't expect to win every point in tennis, right? The GMAT's the same way. So it's okay.)
These two articles may also be useful for you:
http://www.manhattangmat.com/stress-tips.cfmhttp://www.manhattangmat.com/strategy-series-stress.cfmTry some of the strategies described and see if you can find some techniques that are useful for you.