Windows Virtual PC
Support: Configure BIOS
XP Mode only working for processors with Intel Virtualization Technology (Intel VT) or AMD Virtualization (AMD-V) technology.
If you are not sure of your configuration, have a look here:
How to confirm your PC can run Windows XP Mode
Although OEMs have been shipping hardware virtualization in PCs for three years, hardware virtualization is not available in all PCs — so even if your PC is new, it may not have hardware virtualization. Additionally, those PCs with hardware virtualization have it turned off by default, so you will need to turn on the hardware virtualization capability before you can use it.
To determine whether your PC works with Windows XP Mode:
Step 1. Does my PC have a CPU with support for hardware virtualization?
For Intel processors:
1 Download, install and run the Intel Processor Identification Utility. http://www.intel.com/support/processors/tools/piu/
2 Navigate to the CPU Technologies tab and read the value in the "Intel Virtualization Technology" field.
A If the value is No then your CPU does not support hardware virtualization.
B If the value is Yes then the CPU supports hardware virtualization. Go on to step 2 below
For AMD processors:
AMD Virtualization Compatibility Check Utility. http://support.amd.com/us/Pages/dynamicDetails.aspx?ListID=c5cd2c08-1432-4756-aafa-4d9dc646342f&ItemID=172
Step 2. Does my PC BIOS support hardware virtualization, and is it turned on?
Instructions to turn on hardware virtualization in your PC BIOS are specific to OEM models. It is important that after changing your BIOS settings the PC is completely shut down at the power switch before restarting so that the new BIOS settings can take place.
Examples for some models of some computer manufacturer’s BIOS settings are below:
Sample instructions for your PC
Dell systems
Depress the F12 key when boot menu text appears at startup
Select BIOS setup and depress the Enter key
Using the mouse, expand the Virtualization Support menu item by clicking on the plus to the left of Virtualization Support and select Virtualization
Check the Enable Intel Virtualization Technology checkbox
Click Apply
Click Exit
Shut down and restart your computer
HP systems
Depress Esc key when prompted at startup
Depress the F10 key to Configure BIOS
Scroll to System Configuration using the arrow keys
Select Virtualization Technology and depress the Enter key
Select Enabled and depress the Enter key
Depress the F10 key to save and exit
Select Yes and depress the Enter key
Shut down and restart your computer
Lenovo ThinkPad systems
Depress the blue ThinkVantage key when prompted at startup
Depress the F1 key to enter the BIOS setup utility
Using the arrow keys, scroll to Config and depress the Enter key
Scroll to CPU and depress the Enter key
Scroll to Intel ® Virtualization Technology and depress the Enter key
Select Enabled and depress the Enter key
Depress Enter key to continue
Depress F10 key to save and exit
Select Yes and depress the Enter key
Shut down and restart your computer
Please note the instructions above may not work in all cases and consulting with your computer manufacturer may be necessary.
Source http://www.microsoft.com/windows/virtual-pc/support/configure-bios.aspx