computer lagging help!!!

computer is lagging.everytime when i open something.it start lagging a little bit than it stops.

What are the computer specifications. How long has this been happening?

just started few days ago

Could be malware running on your system. Post a HijackThis log in the malware removal forum.

okay.

what should i say? just post a hijack this log?

Follow the instructions there, when done, post back.