I have a Dell c840 and yesterday a student put a password on the computer while I was gone. Now when i turn it on the grey and white screen administrator password protection screen comes up. I have looked at some of the other threads to see if there solutions will work for me. I have tried the DST CD ISO Cd but it will not boot from The Cd apparently. I put in it in the drive and hit f12 and the screen still comes up. Is there any thing I can do to get rid of this.

"Is there any thing I can do to get rid of this?"...

Yes, ask the student what the password is

[takes out sledgehammer] here, try this lol. not sure, ive never had to try this, but if its a desktop, ive heard taking out the CMOS battery for like a minute can fix it. if its a lappy, then i have no idea because i have absolutely no experience with them

while your computer is booting up, try openning your computer in recovery mode, then you cn reset your password, you have to know a little bit of code, but if you look around on the internet and you should find a site that will tell you how to