Administration login problems

I am having logging on problems with my administrator account on vista. I
have an administrator account, a normal account and the default guest account
which is never active. Firstly I tried logging on a few weeks ago and my
password had misteriously changed itself. I had to go into the normal account
and set up a new administrator account while deleting the other one. I could
not fully delete it as windows won't let me fully delete it. The name of the
account still remained in the users folder in the c: drive.
I continued operating under the new admin account until the other
day when I couldn't log on again. The password was changed yet again. I tried
to repeat my earlier actions but when I tried to access any User accounts
options in the normal account none of them opened.
The next day I tried to access my account again on a whim and I was
able to log on with my same password. This time however all my settings had
changed. For example my background picture was back to the default one, icons
were missing off the task bar, etc. Also a seperate administration account
had appeared with all my (music, video, etc.) files in it. Upon checking the
users folder on the c: drive in my computer I have several user accounts,
administrator, normal, mcx1, public, Temp, temp.gary(name of the laptop),
Peter, P.G.(P.G. being my initials.) When I look in Peter and P.G. there are
no files. However, when I try to delete them it attempts to send some files
to the recycle bin (a few 100 megabytes) and then tells me it can't delete
them because they are in use.
I was afraid it was a virus as I noticed some slow down in the
performance over the past week. I have now run 2 anti virus programs, McAfee
which is installed and then Symatec later on, and they have found nothing.
This has left me baffled as I was sure it was a virus causing this touble. If
you could help me I would be so grateful. Thank you so much for taking the
time to read this.