I am afraid that the provided information is not enough to find the reason for the issue. Would you please provide the following information:
1) Did the behavior changed after an upgrade to the latest release (there were changes considering the Alt there) ? If so, test the code with the old dll to find out whether the issue is actually related to the code of the tooltip or to the environment you use.
2) Provide very detailed explanation of the actual and the desired result - as far as I can see on your screenshot there is a RadToolTip and you say that it is not showing.
3) Provide the code of the tooltip and the target so that I can test it on my side.
Once I receive this information, I will do my best to help.
All the best,
the Telerik team