Thank you for your valuable replies !
I'd love to reinstall it, but it seems that I am not uninstalling it properly. Here's what I did:
1) Tried to uninstall it - but Windows can't open the uninstallation log and states that it can only remove the application from the uninstallation window...
2) I manually deleted the mIRC directory, then tried to find all registry entries with "mIRC" and deleted them.
Result: still no luck.
I had similar problem with Pirch98 a year or two before, that's why I'd love to know how to correct it without reinstalling Windows...
Although I am not a programmer, but it seems that mIRC writes its registry entries in such a way, so not all users of the machine can use it. When I am connecting to the Internet, Windows automagically changes users (?) and so the system is using different part of the registry.
If I am right, this would explain why the mIRC icon is blank and why I can use mIRC if I install and start it before connecting to the internet.
Can you tell me, how to fully (and manually) uninstall mIRC, or is there any other way to fix the problem, please ?
thank you in advance for your help,