Rpc Server Unavailable On Old Os After Windows 10 Install

HI, I have 2 separate HDDs on my PC, both were running Windows 7 (home and pro)

I decided to upgrade 7 home to the free windows 10, after a lengthy install it completed fine. However when I rebooted my PC to get into 7 pro a login prompt appears before desktop starts saying " rpc server is unavailable "


Ive tried using the repair cd for startup errors

Checked sfc - all files ok


Im unable to get into 7 pro since installing 10... on a different drive.


I am able to access files within 7 pro's HDD *via* windows 10's desktop if this can solve anything.


Help!