retreiving files off of hard disk

One of the computers here at my office had a major meltdown. so far as i can
tell, the power supply, and either the CPU or the MOBO have perished. I
plugged the HD into an external USB enclosure and have determined that the HD
is still in working order.

I would really like to copy the files off of it onto an altogether different
computer. When i attempt to browse the user's documents, i get the error
message "access is denied". So far i've attempted to create an account on the
new computer with the same UN/PW as is on the old HD, and i've logged onto
the new system as an Administrator. neither work for me.

i'm assuming that i can connect the HD as the main drive on a system and log
in that way... my only problem with that is that i don't seem to have an
working system available. And trying to use the new system, i run into an
issue where the computer will not even boot into safe mode...

any suggestions? with as stressed as i am about this ordeal, i'm sure i'm
forgetting to try many different things.
.