Why does Yahoo Messenger 7.5 slow down my computer to a crawl and blocks other programs from working?

This service Runs with several Servers Like Voice ,Cam etc. and it have also Advance Services comparison to older version. It may be There are another Resion Like Virus attack Check Your PC it may be possible there are Some Virus Attack on yr Pc.

Also, keep in mind that sometimes there is a glitch in the communication between programs when Yahoo is running. There are programs out there that use the same files that yahoo uses, and that could cause your problems. For instance Windows Blinds is a program that doesn't always work well with Messenger. Also, check out your processes and see what else you have running. To do this click on control, alt delete to bring up your task manager. This will let you see what is running and how much your using. Also stop those programs that you dont need.