I have been trying to play pacman/tetrix etc. which you can download for free on internet. It tells you to move - using the arrow keys and shoot with your spacebar. This is always ok for the first 30 seconds or so of the game, and then its as though you freeze and you can't move or shoot, but the other objects still come towards you and fire at you but you can't retaliate. Its always ok then when I start a new game. Is there something I am doing wrong?
Sounds like you might have sticky keys enabled...this stops keys on the keyboard being recognised if they get stuck and pressing keys many times can also make this happen....Go into Control Panel then click on Accessibility Options and untick the the sticky keys tick box and maybe tick Filter Keys to see if that helps.
I have something similar with shockwave games, I thinks it's when an ad banner changes on an open window (not necessarily the game window). Minimize all other windows or when it freezes next time try clicking the mouse pointer on the game screen to 'remind' it thats the one you're using and see if that works!
By the way, if all you want is Pacman and Space invaders I use this one with no problems - apart from the 'pong' which is too hard to control with the mouse!