Parallels 7 after El Capitan update
You're going to have to upgrade to Parallels 10 or Parallels 11. See this Parallels knowledgeable article: Parallels Desktop and Mac OS (Host) compatibility

There is a free trial demo of Parallels 11. So you may be able to convert your old Parallels 7 file in advance of paying for it.

Next time you update OS X be sure to check its compatibility with the version of Parallels you're running. Parallels is a program that often breaks with an OS X update.