Can't get my games to run??????

[Easygoing]

I hope someone can point me in the right direction. I have the following hardware: 1.4 AMD, 512 memory, IWILL MB, Gforce3, SB live, running XP professional. I had to reload my system from scratch and now Ghost Recon and Commanche4 won't run. As soon as it gets past the usual menu stuff and where you start to play the game it either reboots the system or goes back to Windows. These games use to work before. I loaded the latest drivers from, nvidia and soundblaster. The lastest software patches from the game support site. Other games such as counterstrike work fine. What did I miss???? Thanks.