I've been playing Source engine games (that means half-life 2, right?) and sometimes I randomly just stop moving, and the sound starts playing over and over again. Finally, after a few minutes the program just shuts off altogether. Sometimes it locks up like this but then resumes normal play. It happens more frequently on 'Garry's Mod' than 'Counter-Strike: Source'. 1.4GHZ Intel Celeron 256MB SDRAM PNY NVIDIA FX5700- 510MHZ Core 711MHZ Memory. Am I on the rim of system requirements?