Sorry you're not doing it right, just took a look at the 22" in our spare bedroom and happens to be the exact model you have! Checked and yes the feature is there.
Plug the computer into HDMI 1 (DVI) - Should be displayed next to the port. This is important as it is the input required to set as PC.
Once done, press Source, highlight the HDMI, press Tools, Choose Edit Name and then in the list presented scroll to and select PC. The screen will flicker and you will now have a nice clear PC picture. This setting actually enables the TV to output the correct PC colour format or something, which is unavailable in other modes apparently and as I said above was the only input to not have a noticeable amount of input lag as I play BF3 through my 46" and the lag was very noticeable in Movie, Gaming and standard mode. Only renaming to PC made it a nice experience.
As said, exact same TV so it is there.