when i start my pc this this message comes'HookAPI.dll was not found'wat i should i do???

When I searched for HookAPI.dll via Yahoo I got some hits that indicate this is part of a Trojan horse. I suggest you dust off and run your anti-virus -- if it still runs. If you find it's not able to run or runs strangely, the malware may have corrupted it. In that case, download and run Stinger from McAfee (it's free).

Stinger is an anti-virus's anti-virus: Its sole purpose is to look for and clean up malware that attack the big anti-virus packages themselves (Norton/Symantec, McAfee (naturally), maybe others). It's so good the publisher has had to change its name a few times to keep the badguys off balance.

Note that it won't repair your anti-virus. You'll probably have to do a reinstall for that.

Good luck.

scan for spyware, look at your startup and disbale some startup items, that could be a trojan or virus and could alter your system