You need to understand source and target server requirement for successful conversion.
Here is some guideline when performing P2V (Physical to Virtual) conversion:-
a) Minimum of 512 MB of memory
b) Same domain as the VMM 2008 R2 server or join to domain with a two way trust domain.
c) Online P2V conversion supported for those operating system with VSS (Volume Shadow Copies). Windows Server 2000 will use Offline P2V conversion technique.
Target server limitation
a) Maximum of 32 or 64GB of memory (based on windows edition)
b) Maximum of 4 processor cores.
c) Maximum of 12 network interfaces
d) Maximum of 2TB disk for any VHD
e) Maximum 256TB for pass through disk
f) Maximum total storage of 517TB using VHD
g) Maximum total storage of 66560TB using pass through disk
Best practices before conversion:-
a) Run chkdsk utility to make sure no bad sector on the hard disk
b) Run defragmentation utility
c) Use 1Gbps to reduce the time to complete a conversion
d) Perform conversion on those server which is low utilization first before convert medium and high utilization server.
e) Temporarily disable Windows Firewall on the source server