Internet explore doesn't start

[bbunus]

I have a PC with windowsXP. I created several users on it. It had been working fine. But a few days ago, two of the users could not start the internet explore, yahoo messenger, or MSN messenger. I clicked the icons, nothing happen. Meantime, other user can start those just fine.

Why is this? How do I fix it.

Thanks!!! :hotbounce