You need to take ownership of that hard drive with the new PC.
select the drive and right click it. Got properties, security, advanced. Go tot he owner tab. Check the box at the bottom (replace owner on subcontainers and objects). Pick your users ID from the top and hit apply.
This will take a while if there are a lot of files.
Your other PC, while it might have had the same user ID for a profile, it is looking for the user ID from that PC. Doing this will reset the hard drive to know it is in a new PC and there is a new boss in town
Hope that works