If you change from a multi-processor system to a uni-processor system you need to manually change the HAL on the Windows server after the conversion.
To do this go into Device Manager after the machine first boots and discovers it’s new hardware and then click on Computer then right-click on the processor and select Update Driver. Then select Install from specific location and then Don’t search I will choose the driver to install. Then select show All compatible hardware and select the appropriate processor.
For example, if you went from a dual cpu to a single cpu then select ACPI uni-processor PC instead of ACPI multi-processor PC. You will need to reboot once you change this. To verify what HAL you are using you right-click your hal.dll in c:\windows\system32 and select the Version tab and select Internal Name and it should say halmacpi.dll for multi-processor acpi and halacpi.dll for uni-processor acpi.
Next clean up all the non-present hardware after the P2V conversion. To do this go to a CMD prompt and type SET DEVMGR_SHOW_NONPRESENT_DEVICES=1 and then DEVMGMT.MSC and then select Show Hidden Devices. Delete any old grayed out hardware. Next remove any vendor specific applications/drivers. For example on a HP server you should go to Add/Remove programs and remove any HP management agents, survey utility, array config utility, version control agent, etc.
Also check your NIC and make sure there are no vendor specific drivers there (ie. teaming). Check the Services to see if all there is anything vendor specific related there and disable any services that are.