[meford4u]

If it's block then you definately only have strapping holding up the drywall. That's why you can't find a wood stud. The strapping should be every 24" on centre, so start from a corner and measure outward and you should be able to tap and find the strapping. Hope it's just for picture hanging and not something like a shelf you want to hold up. If it is something heavier, use a butterfly spring that you will have to drill into the block wall with a 3" or so screw. That will hold just about anything.