ExcelBanter - "Disappearing" Worksheets

Hi guys,

I've only known this problem on my pc at work.Wonder if you could help me?
Occasionally a worksheet will just totally "disappear" leaving a blank grey
screen although I know the sheet is still there. If I type a cell number
into the Name Box, then it will show me correctly what is in that cell.
There is nowhere that I can see to "maximise" back the worksheet. Bizarrely,
occasionally I will be able to Right Click on the Task Bar maximise from the
menu but more often this option is not open to me although sometimes that
option will appear 10 or 30 minutes later although I haven't done anything
to change the situation to my knowledge.
Another strange phenomena that occured is that I plugged in my memory stick
and the screen magically reappeared!
I have to send a worksheet via email to my boss on a daily basis and he
often replies that he can't see the sheet either. I asked him to try and
save first, then open but this didn't work. He says that it is only the
files I send that give him this problem.
I sent a test file to him and a colleague. My collegue opened the file no
problem but the one sent to my boss didn'nt!
I have done a full virus scan on my pc but no problems showed up.
Any ideas? Thanks!!!