Windows XP- Go to the Start Menu and click "My Computer"
- Open you C:\ drive
- Open "Program Files"
- Look For a file that says "Blockland"
If its not there re-download Blockland
Windows 7 Similar minus one step.
- Go to the Start Menu and click "My Computer"
- Open you C:\ drive
- Look For a file that says "Blockland"
No "Program Files" this time (same procedure if it's not present)
Linux: Ubuntu 10.4- Go to Places and click "My Computer"
- Select "File System"
- Go to the "usr" file
- Select "Games"
It should be there, if not refer to the "Re-download Blockland" idea at the top of the post.
I covered 3 OS's here, I don't own a Mac though so I can't help you with that.