First of give us all info you can get ,
1. What system you have cpu/motherboard/ram/ect ect
2. what Windows you have ?
3. what game ?
4. what video drivers you useing ?
EDIT: if you haveing problem only in Mplayer mode maybe your windows screwd up , are you trying to play Online via DSL/Dial Up or Over LAN/Serial connection ???
.:. Lian Li X500FX .:. i7 2600k .:. PNY GTX 680 .:. Corsair DDR3 8GB .:. Silverstone 800W PSU .:. Asus P8P67-M Pro .:. Crucial M4 SSD 512GB .:.