Currently my VLC player is playing all my videos with only audio but no video (its just a black screen!)

How can i fix this?

I use a Windows XP Home Edition with Service Pack 3Reinstall VLC player.........If that doesn't work, try reinstalling your video driver in device manager..

Click Start, right click on "my COMPUTER", click "properties", click "hardware" tab, click "device manager"

Click on the "+" sign next to "display adapters", right click on the item in the submenu and click on "UNINSTALL"....Restart the comptuer and windows will reinstall the driver automatically .... Make SURE you are using the latest version of the driver as WELL...Open VLC - go to TOOLS - PREFERENCES - at the BOTTOM put a tick in Show ALL - Click on the VIDEO setting - remove the tick from OVERLAY VIDEO OUTPUT

Did that help?It helped, but now my videos are incredibly laggy, is this normal?
No. Check the other video settings (play with them a little). Also, try GOM player - I actually prefer it to videolan.
Im not good at "playing" with video settings

Does GOM player play .mkv files well?

http://www.gomlab.com/eng/forum.html?mode=viewpost&c=5&f=2&t=729&pType=0