I thought it might be an issue with your sources.lst, but it's not. It looks like it has been installed.
I'm not sure the problem, but you can try:
Those will just tell you the location of the install. I'm not sure why restart isn't working.
Falko told me to follow this installation howto for Wheezy, and I didn't have any issues: http://www.howtoforge.com/perfect-se...ot-ispconfig-3