I'm using VB5 SP3.

I'm encountering a very and the most frustrating problem for the 1st time. When I tried to change some code in VB, some lines disappears or overwrites each other. So I tried to delete the whole function to rewrite it. I can't even delete it! The whole application hangs if I try to 'Undo' changes.

Has anyone has this problem? How can I fix it?