After a Windows 10 Update (done automatically) Windows 10 was not able to use the full resolution of the iMac. Win10 shows that the maximum resolution is 1920x1200. When I use this resolution, Win10 uses most of iMac screen except that it does not use two regions on the left and right of the iMac monitor. The only way I have been able to make it use the whole monitor is when I set Parallels to "Scale to fit the screen" but that looks ugly because all fonts are stretched. Before the Win10 upgrade all was fine and beautiful. How I can get Windows 10 to use all iMac real state screen when in full screen. By the way the "Use OS X Full Screen" option is checked. I also discovered that Win10 does not longer opens in Coherence mode; the starting hour glass remains working for ever, and if I click on "show" it display the regular no-coherence screen. I just payed the money to upgrade Parallels from 11 to 12 and I wasted my money because it did not change the behaviour.
It seems that Parallels company avoids putting a support phone or chat because it cannot be found anywhere in this support pages, but I found it another way: the support phone for North-America is (425) 282-6400. A representative helped me to resolved this problem. If you call, make reference to Support Call Ticket Number 2334421. He first tried Actions --> Reinstall Parallels Tools, but it did not work, so he ended up downloading and reinstalling Parallels 12, and then reinstalling the Parallels Tools and that made it work again: Win10 sound that was not working now works, Win10 finally opened in full screen using all iMac Monitors real state and the resolution is back to 2560x1440, and now I can switch to Coherence mode any time, before it was greyed out.
Thanks a lot for sharing this info. Parallels Tools installation helps to resolve issues with Coherence/Full screen modes. with sharing between Mac and VM and etc. BTW you may contact Parallels Support here, on the Facebook or Twitter and using this link (you need just click "Show all" on the end of the page, then you will be able to find the numbers to call and Email support option too)
