Sorry, the issue is somewhat too vague to be able to help you properly.
But, try one of the following:
1) Go to Control Panel -> Java -> (General Tab, Temporary Internet Files) -> View -> (Find all Batclient -related applications, click on them and press X to delete).
Then reload Batclient from our website at
http://www.bat.org/play/batclient/2) Another thing, which might help is to delete/rename the whole batclient -directory from your local user directory (of course you will lose all settings, triggers etc. which you may have saved).
3) Go to Control Panel -> Java -> Advanced -> (Settings) -> Java console -> (tick) Show console
and then re-start Batclient: a debugging console view will pop up asides Batclient, which may lead you further towards the root of your problem.
I hope this helps.