Install Windows 7 x64 drivers for PS/2 to USB adapter
Most PS/2 to USB adapters works perfectly on Windows XP. Most times this adapters have problems on being detected by Windows 7 and Windows Vista.
The biggest problems are common on 64-bit versions of these operating systems.
If you have problems with properly detecting PS/2 to USB converter, try to disable UAC in Windows 7:
How to disable UAC in Windows 7
After you complete the steps above, insert PS/2 adapter in USB port and see if it is detected by Windows.
Allow Windows to detect the required drivers and install them or to suggest the manufacturer website for their installation.
Once the correct drivers are downloaded and installed, the adapter should work normally.
If Windows won’t detect the adapter, is because the adapter, most probably, is not compatible with your new operating system.