Maybe try looking for "Explorer" under start->Programs->Acessories, and right click it and select "Run As Administrator" and try again?

Otherwise you can try enabling the true adimistrators account (in the tutorial section of this forum) and log in as administrator and try it from there.

Though... it's probable that the access denied is because... in order to to ANYTHING with those files, anything at all, you need to be the identical user with the credentials from your old 32 bit install