delay in opening an excel file in excel2007 from the explorer wind
 

I have a peculiar problem with excel 2007 in one of my pc's.
When I try to open an excel file from an explorer window, it takes a long,
long time for the workbook to open. This is true both for xlsx and xls files.
However, if I first open the application excel 2007 and then open the excel
file from within the application menu, then the workbook opens without a
delay.
What could be the reason for this odd behaviour? I have looked into the
settings and tried to figure out the reason for this odd behaviour. Without
much success so far.
I would be grateful if I can get help in solving this problem (actually,
this is a problem not just with excel but with all office 2007 applications).
The problem is particularly acute when I try to open an attachment that I
have received by mail.