Reboots to desktop

HI ya Gang, EX-Flybill here, I could not log in under my old username, anyhow, I installed fs2004 and WOW, what a big difference, I love it!!. The only problem is that when Im on a long flight, about 3/4 into the flight, my computer reboots to the desktop, I have a 2.8+ghz athlon, 512k 2700ddr ram, Nvida 64pbx8 card, running windows xp sp2. All my drivers on everything iis up to date. I'd shut down all running apps that I could before I started the sim. Also, I dwnlded some 2004 aircraft and zipped them into the aircraft folder, but some of my planes that I downloaded are not showing up in the list. Can anyone help me with my 2 issues? And can someone suggest a real good, step by step site on navigation? And good 2004 aircraft download site? And last, Can anyone recommend a good freeware Aircraft installer program so I can install aircraft, textures..etc, program? OK, getting off my soapbox..LOL Thanks Bill, You can also email me at: PREACHBILL@AOL.COM