hi.....suhas ...
i hope the problem u mentioned mite b due to some processes related to game are running in the background ... even if u had exited game .....
if u can access the task manager (ctrl+alt+del).... check 4 the processes .......
and also try this once .....
instead of ending the game .... minimize the game and try to end the game by ending the corresponding process from the task manager .....
now check whether u can access the system or not ....
and do post whether the problem is still existing or not (by ending the process also ) ....