I have been running Windows 10 Tech Preview for quite a while now on my Dell Venue 8 Pro and I still love it and use it daily. Granted, I do not do many wildly demanding tasks but I do use it to listen to Pandora and to read ebooks and some other simple stuff and I am really digging it. This weekend, though, I had an issue which I guess started after an update was applied and a reboot occurred, my tablet booted to the login screen, after I logged in it went to just a black screen, I actually made it start up in recovery one time and had it drop back to an earlier build and it booted right up, then I guess the updates came in again and the following morning it was back to the black screen. This time I could not get recovery mode started no matter what I tried. I did have an external keyboard, non-bluetooth, hooked up and could get it to start task manager. No matter what I tried the programs I tried to fire off did not fire up, like cmd or control or even msconfig, everything just did not show up…..explorer wouldn’t even start up. So I figured I would use my backup to go back to an old build, as soon as I plugged in the USB drive while at the task manager the programs I tried to start actually started to fire up. Then the tablet rebooted, I guess to try to fire off the Backup Recovery app, my tablet has been booting fine ever since. I have no idea why it actually worked, but thought I would share my experiences just in case someone else had issues like this. I am on the fast track for getting updates which is probably part of my issue, but it is just my tablet and it is not mission critical.
EDIT (5/5/2015): Ok, seems that this issue has happened again, but task manager could at least fire up control panel, I had 3 updates that were installed and one of them was KB3061162, which I could not find any info on. I uninstalled it just to see and my tablet booted right up as it should have, weird, but hey it is a Beta…preview…or whatever it is now. Still do not think it is bad enough to go back to Windows 8.1.