Problem Updating Links

I have a workbook (created by someone else...ugh) that uses links to another
workbook (an answer sheet), no longer available. I have a new version of the
answer sheet, but when I try to edit the cells in the first workbook, they
will only display the formula itself of the actual link.

e.g., the cell displays: ='[ITEMS for MC TABLE REV1.xls]ITEMS SORTED'!$F$12

Nothing short of Edit/Clear/Formats seems to let me redo these links. Oh, it
lets me change the link, but then simply displays the link as text, just as
it did the previous link. Also, I can't even add a new link anywhere on the
worksheet, until I clear the formats. One clue might be this: the cells in
question are set to Text format, as the text is a decimal number (such as
415.99). I've tried just changing the cell's Number format to something else,
but no joy. I've also tried unprotecting cells, the sheet, unlocking cells,
etc. No joy.

Any ideas?