Hi Aghoribj,
Parallels Desktop 8 is not compatible with OS X 10.10, It may stop working anytime together with Yosemite updates - as Parallels Desktop 8 is not optimized for this OS. If you would like to continue using your Virtual Machine on Yosemite, we recommend you to upgrade to Parallels Desktop 10 for Mac. You may find information on what's new in Parallels Desktop 10 for Mac at http://kb.parallels.com/122698