Help!!! I get "Access Denied" message .........

Hello all!
My problem is I get an "Access Denied" message that further states "Please
login with administrator privileges and try again". I AM THE ADMINISTRATOR!
I can't go any higher. I have all rights and privleges enabled under my user
account. I even went so far as to go into safe mode, login as
"administrator" and double check and of course it has my account as having
full control and administrative rights. I just recently installed XP Home's
SP2 and after I did that it started doing this "Access Denied" B.S.! It
acually doesn't effect much and has only happened a few, completely different
times but with a non-stop consistancy. Once when I went to install a program
(SIMS 2) it wouldn't let me but after I logged in to the actual
"administrator" account (in safe mode)and I double checked that I had full
privledges and I did, I logged back into my origional account (my account is
considered a "User/Owner" account with full administrative privledges) and
the game installed fine. And yesterday when I installed Microsoft's own Rise
of Nations game and go to play it I get another stupid "Access Denied"
message that I wrote earlier. I'm getting fed up with this after 10 or so
hours of searching the MS's KB and tinkering with settings and reading fourms
and various trouble shooting just to play a game!
Usually I can figure out the problem on my own but this is....well a
problem that has stumped me (for now) and you guys/gals seem to be on top of
this game. Could you all help?

The system is a newer Dell laptop and I just reformatted and reinstalled
Windows Xp Home and am currently tring to reload all my applications and
games. I've run various tests on the hardware and hard drive just incase it
might have been a hardware issue but everything checks out. Like I said this
all happened after I installed SP2. Thanks