My shell responds with:
sed: command garbled: s/\(#\)\(/dev/sde1.*\)/\2/
You need to escape the / character... like this:
sed 's/\(#\)\(\/dev\/sde1.*\)/\2/' /etc/fstab
sed 's/\(#\)\(\/dev\/sdf1.*\)/\2/' /etc/fstab
The only difference is the sde vs sdf... regular expressions would allow you to process them with just one line. But if its a one time execution, save yourself the trouble.
You're welcome PoM...

There is another one for Awk floating around somewhere.