Host hangs during bootup after installing Hyper-V Role

My hyperv test box is a Dell Optiplex 980, i7, 8GB RAM.

Due to small data partitions I had to rearrange the partitions on the disk.

Before this the layout was like this:

#1 primary WS2008R2SP1
#2 primary WS2012 RTM Build9200
#3 primary ext3, boot partition
#4 extended
#N logical WS2012R2 RTM Build9600, booted from #1
#N logical WIN data partition with VM images

System was booting from #3 into grub, which did chainload into #1, #2 and several logical paritions.

Now the layout is like this:

#1 primary ext2
#2 primary ntfs, boot parition
#3 primary linux-swap
#4 extended
#5 logical WS2008R2SP2
#6 logical WS2012 RTM Build9200
#7 logical WS2012R2 RTM Build9600
#8 logical WSBeta1, empty
#9 logical WSBeta2, empty
#10 logical WIN data , now large enough, still empty
#N logical several ext3 partitions

First I installed WS2008R2, installed role Hyper-V, applied all updates. Everything looks fine there.

Then I installed WS2012, system came up fine. Then the trouble started: first installed role Hyper-V, after several reboots during role installation the box is hanging with busy HDD LED. Not sure if there is actually disk activity. It booted up to the turquoise squares which are initially shown. But those white spinning points are not shown. After one hour I did a hard reset, installed WS2012 again and applied all available updates before attempting to install the role Hyper-V. But unfortunately same result.

Then I figured this bug might be fixed with WS2012R2. So same procedure, install WS2012R2, apply all available updates, system comes up fine. Install role Hyper-V, several automatic reboots during role installation. Result: same hang with busy HDD LED.

I'm not familier with the Windows boot details.

So my question is: What debug data can I provide so that someone familiar with the boot sequence of a Windows host can see how far it got? Are there any logfiles written, and hopefully flushed to disk, to see how far in booting it got? I remember in the startup properties there are knobs for serial ports. I will enabled them from the WS2008 partition, maybe some useful progress log is written to the serial port.

Over night I will let it run, maybe WS2012R2 recovers after a few hours.

Thanks for any help with tracking this windows bug down.

Olaf