By default, Excel changes hyperlinks to relative path. So, entering an absolute path in a link is generally a waste of time. Yes, you can write the link using the HYPERLINK() function, but that is a hassle. Here's how to force Excel to respect absolute paths...
For a workbook: navigate to File | Properties | Advanced Properties | Summary tab, and set Hyperlink Base = C:\. Excel will no longer alter paths for future versions of that workbook. (You will still need to visit each link and edit in the absolute path.)
To set absolute path links for all new workbooks, save the above change in book.xltx. For Excel 2010, that file should be created in your home folder (usually C:\users\(your name) at AppData\Roaming\Microsoft\Excel\XLSTART.
For a subset of new workbooks, do this on a specific template, and call that template to create the workbooks.
PS: I have seen it said that absolute paths are a bad practice. That is true for objects that move as sets (like programs and help files.) It is not true for documents shared to personal folders that link to shared folders. That causes broken links.
PPS: This does not seem to affect sheet to sheet cell references. These seem to always reduce to relative paths when the referenced sheet is opened, and always convert to absolute paths when the reference sheet is closed.
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