Unable to start ARMA II and ARMA II: OA

[Mocah 0]

So hey, I been having a problem where I can't get into both ARMA II and ARMA II: OA, I've been trying the whole admin thing, but I'm using XP so I can't exactly start it. When ever I try to use "Administrator" It requires me to type in a password every time, but I can't exactly find it since I have no idea where to find Administrator and change the password to it. I'm logged in as an Admin for the account I'm logged into, but I still have the problem where it doesn't recognize that I am. It doesn't come up with any error messages though, it just the whole check mark thing when you start it up, and only go to all the other check marks except the last two, then once it reaches the second to the last in a Millisecond it just disappears, there's nothing, no window at the bottom saying its there, it just disappears into thin air. I really don't know why it does this though, if someone could help me it would be much appreciated. ~ Mocah