Can't open more than one file.

[adnum8]

I have looked and looked but only seen one or two vague references to this problem.
This has started only recently...I can only open one excel file at a time. That is, if I have an excel file open and I click on another, the first one closes. I used to be able to have multiple excel files open.
I am starting to think it may be a memory problem but don't know how to prove it. (Using win98). Thanks for any help.