Game crashes while playing

so i bought Ns2 because it was cheap on steam after downloading i started the game up no problems but after playing for about 10 to 15 minutes the game crashes.
i have tried all the fixes i could find but none work.

PC Specs

OS: Windows 7 Ultimate SP1
CPU: Intel Core 2 Duo 3.0 GHZ
GPU: Nvidia GT630 1GB
RAM: 2GB DDR3