squirt,
Is your worksheet filtered? (I know that's sort of obvious, but if it is, my suggestion wouldn't be useful at all). Filtering will hide rows that remain hidden when choosing Unhide Rows, because the filter is still applied. To turn off filtering, select the Data menu, then select Filter, and see if either autofilter or advanced filter has a check-mark by it. If so, un-check it, and your rows should return.
If that's not the solution...
Assuming that the worksheet isn't filtered, try selecting all of the rows&columns with data, extending past the missing cells, and paste into a new worksheet. You should at least be able to see what's there and what's not there, and may be able to re-construct the original sheet.
Hope that helps,
Cindy