When I use Shift+F4 to change a relative address to an absolute address, nothing happens.
Look in Tools | Customise and click on the Keyboard tab. Scroll down and make sure Shift-F4 is linked to Relative/Absolute references; if not that function can be found under the Insert category below.
For the new version, just use F4.
From version 5.1 (see tdf#59418).