Yahoo messenger not showing text in chat box

Here’s a solution which will almost certainly solve your problem. Click: START
Click: RUN
Type: REGEDIT
PRESS ENTER
Locate: HKEY_CURRENT_USER > Software > Microsoft > Windows > CurrentVersion > Internet Settings > Zones >
Youll see a number of folders numbered: 0 1 2 3 etc
Above these you might see another folder there, before that zero folder, with a box type character - delete that .
Now close and Restart Your Pc everything should be fine.
If not, try uninstalling Messenger and then doing the above then reinstalling
Hope this cures your problem and let me know.