I suspect it has little to do with the size of the file. Excel files
corrupt over time. Often associated to the 'Normal' style.
It is also possible that you have corrupted the toolbar customisation file.
This is named xxxxxxx.xlb. The file name changed, but the extension .xlb
has been constant.
I would start by renaming the one you have. Excel will create a new one,
but any changes to your toolbars will be lost. If this works, you can
delete the old file. If not, rename it back and any customisations will
return.
Next, try opening the file in XL2002/3. If you can find someone with it.
(You may already have it of course). These versions are much better at
handling crashed files.
If not, you could try opening it in Word or similar. You will lose your
formulas, but will get the data back.
There are probably many other ways, but here's a few to help
