Strange problem while execution of query....

Hi Friends

I am facing a strange problem while executing the query.

I have one query ,its old one ,till yesterday everday it was working fine ,

But today i am trying to execute that query ,execution process takes very long time ,finally no response from bw server.

its an important report in our company

I checked query , Every thing is ok ,bze i haven't made any changes

So i need some suggetions .like where can i check and what can i do?

ASAP .... So Please ...its very urgent....

EVERY THING AND ANY THING WILL BE REWARED

Thanks in advance

RK