Hanging up on opening screen

Having problems getting game to load. Installed it with no problems. Have played several times with no problem. THEN- without any apparent reason whenever i try to play it again it gets hung up on the opening screen (no error message, just the opening screen for all of eternity). When I ctl+alt+del it shows that the program is "not responding". HELP!!!!!!! Here's my specs: Dell DX260 with Pent 4 (2.40 GHz), 1.5 Gig RAM, XP svc pack 2, 11 gig avail disk space. I tried reinstalling- same thing-works 5 or 6 times with no probs-then back to hanging on the opening screen. Have also tried "repair" function with no effect (doesn't correct the hang). I have installed a few add-ons from this site (aircraft) but have flown them successfully prior to the problem occuring so I don't think it's that.