Can I restart the level from the beginning without restarting the whole game..?
Sorry it took so long to respond. Yeah, you can restart the level if you want, but there isn't any option to do that through the game itself....You'll have to replace your .sol (save) file with the one for the prison cell location (#4) from this thread:
http://forum.amanita-design.net/index.php?topic=1274.msg6092.htmlAnd here are instructions for finding and switching the Machinarium.sol file on your computer:
http://forum.amanita-design.net/index.php?topic=1095.0.html