| I know this is a long shot, but here it goes: I just tried to convert a Virtual Box (Windows) VM to qemu. 
 I've followed these steps: https://utappia.org/2016/04/20/how-to-m ... rtmanager/
 
 I had no errors during the process and my converted qcow2 HD seems to be OK:
 
 
       Code: 
finottim83[~/qemu]$ qemu-img check Win7_64bit.qcow2
 No errors were found on the image.
 540340/542544 = 99.59% allocated, 0.00% fragmented, 0.00% compressed clusters
 Image end offset: 35417423872
 
 
 finottim83[~/qemu]$ qemu-img info Win7_64bit.qcow2
 image: Win7_64bit.qcow2
 file format: qcow2
 virtual size: 33G (35556163584 bytes)
 disk size: 33G
 cluster_size: 65536
 Format specific information:
 compat: 1.1
 lazy refcounts: false
 refcount bits: 16
 corrupt: false
 
 
 
 I made sure that my "Disk Bus" is "VirtIO" and the format is qcow2.
 
 But I get "No bootable device." error message.  (I'm using virt-manager, BTW.)
 
 You can see some configurations of the VM here:
 
 
       Code: 
finottim83[~/qemu]$ virsh -c qemu:///system dumpxml win7
 <domain type='kvm'>
 <name>win7</name>
 <uuid>3f0ed739-cdd3-4a5d-8423-615730687e26</uuid>
 <memory unit='KiB'>20578304</memory>
 <currentMemory unit='KiB'>20578304</currentMemory>
 <vcpu placement='static'>4</vcpu>
 <os>
 <type arch='x86_64' machine='pc-i440fx-2.7'>hvm</type>
 <boot dev='hd'/>
 </os>
 <features>
 <acpi/>
 <apic/>
 <hyperv>
 <relaxed state='on'/>
 <vapic state='on'/>
 <spinlocks state='on' retries='8191'/>
 </hyperv>
 <vmport state='off'/>
 </features>
 <cpu mode='custom' match='exact'>
 <model fallback='allow'>Haswell-noTSX</model>
 </cpu>
 <clock offset='localtime'>
 <timer name='rtc' tickpolicy='catchup'/>
 <timer name='pit' tickpolicy='delay'/>
 <timer name='hpet' present='no'/>
 <timer name='hypervclock' present='yes'/>
 </clock>
 <on_poweroff>destroy</on_poweroff>
 <on_reboot>restart</on_reboot>
 <on_crash>restart</on_crash>
 <pm>
 <suspend-to-mem enabled='no'/>
 <suspend-to-disk enabled='no'/>
 </pm>
 <devices>
 <emulator>/usr/bin/kvm</emulator>
 <disk type='file' device='disk'>
 <driver name='qemu' type='qcow2'/>
 <source file='/home/finotti/qemu/Win7_64bit.qcow2'/>
 <target dev='vda' bus='virtio'/>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
 </disk>
 <controller type='usb' index='0' model='ich9-ehci1'>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x7'/>
 </controller>
 <controller type='usb' index='0' model='ich9-uhci1'>
 <master startport='0'/>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0' multifunction='on'/>
 </controller>
 <controller type='usb' index='0' model='ich9-uhci2'>
 <master startport='2'/>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x1'/>
 </controller>
 <controller type='usb' index='0' model='ich9-uhci3'>
 <master startport='4'/>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x2'/>
 </controller>
 <controller type='pci' index='0' model='pci-root'/>
 <controller type='virtio-serial' index='0'>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
 </controller>
 <interface type='network'>
 <mac address='52:54:00:f5:da:18'/>
 <source network='default'/>
 <model type='rtl8139'/>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
 </interface>
 <serial type='pty'>
 <target port='0'/>
 </serial>
 <console type='pty'>
 <target type='serial' port='0'/>
 </console>
 <channel type='spicevmc'>
 <target type='virtio' name='com.redhat.spice.0'/>
 <address type='virtio-serial' controller='0' bus='0' port='1'/>
 </channel>
 <input type='tablet' bus='usb'>
 <address type='usb' bus='0' port='1'/>
 </input>
 <input type='mouse' bus='ps2'/>
 <input type='keyboard' bus='ps2'/>
 <graphics type='spice' autoport='yes'>
 <listen type='address'/>
 <image compression='off'/>
 </graphics>
 <sound model='ich6'>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
 </sound>
 <video>
 <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
 </video>
 <redirdev bus='usb' type='spicevmc'>
 <address type='usb' bus='0' port='2'/>
 </redirdev>
 <redirdev bus='usb' type='spicevmc'>
 <address type='usb' bus='0' port='3'/>
 </redirdev>
 <memballoon model='virtio'>
 <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
 </memballoon>
 </devices>
 </domain>
 
 
 I could install a Debian ISO into a new VM without problems.
 
 Here is some info on the system:
 
 
       Code: 
finottim83[~/qemu]$ infobash -v3
 
Host/Kernel/OS  "finottim83" running Linux 4.8.0-6.slh.1-aptosid-amd64 x86_64 UEFI64 [ aptosid 2013-01 Ἑσπερίδες - kde-full - (201305050307) ]
 
CPU Info        8x Intel Core i7-4790 @ 8192 KB cache flags( sse3 ht nx lm vmx ) clocked at [ 3694.262 MHz ]
 
Videocard       Intel Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller  X.Org 1.18.4  [ 1920x1200@59.95hz , 1280x1024@60.02hz  ]
 
Network cards   Intel I217-LM
 
Processes 334 | Uptime 23:03 | Memory 7196.3/31977.3MB | HDD Crucial_CT512M55,WDC WD5000AAKX-0,ATAPI-6 Bridge C Size 2012GB (23%used) | Client Shell | Infobash v3.50
 
 Any ideas or suggestions?
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