Whats wrong with my ym?

after being online for some time, when someone IMs me, i cant see what he/she is saying and it just looks like a box pops up. it makes all the pictures in photoshare extremely minute, prevents me from sending and receiving files, and disables me from viewing my message archive until i end yahoo messenger and restart it. but then itll all happen again after a while. my mcafee virus scan wont detect anything and ive tried uninstalling and reinstalling yahoo messenger several times but to no avail. there is still something wrong with my YM. anyone know what though? and moreover, how it can be fixed? thanks.