System hangs up frequntly. Updated all drivers and MS updates using windows update, but still the system keeps hanging frequently.

Event viewer shows as below:

"Source : Srv

Type: Error

Event ID: 2019

Description: The server was unable to allocate from the system nonpaged pool because the pool was empty."

PC Details:

DELL OPTIPLEX 755
INTEL CORE2DUO 3.00 GHZ
4GB DDR 160GB SATA HDD
MATROX 4OUTLET VGA CARD

<ADMIN NOTE: Service Tag removed per privacy policy>

Please help me to solve this problem.