Yahoo messenger

Can anyone shed any light on this sign in problem I have with yahoo messenger. It was the first IM I had on my PC and it worked fine then. Then I deleted it and Installed msn. Then I got hijacked by CWS and others Including PSguard and desktop taken over. Last night I Installed it again and every time I try to sign in it fails. Despite the fact that I am signed into yahoo mail so my user ID's are valid and I've been meticulous about typing them in. Why won't it recognise the valid ID. I just got my PC cleaned out with the help of one of the TC volunteers so there should be no problems with other programs. Advice please. <_<

Uninstall yahoo once more, this time afterwards delete the folder C:\Program Files\Yahoo Messenger, and reinstall it

Will do. Was thinking maybe it was remnants of last Install that was hampering. Willtry that. Cheers.