Actually, I don't think this problem would have to do with the autoexec.bat file. It is just a batch file that runs the same commands over and over every time the computer boots. The autoexec.bat file would have to contain a line that initiates another file to run. This file is probably a *.sys, *.exe, *.com or a *.bat file.
To get rid of this problem you must determine WHAT the file is, WHERE the file is, and HOW to get to the file. If it comes up on your screen before the desktop is activated then you will probably have to boot your computer from a floppy or cd-rom and work your way through dos to find the file. Dos? Oh, you have a mac, I'm sorry. That would mix the situation up. lol.
Now, here is where WHAT type of file and WHERE the file is that can make or break your day. Don't delete that file!!! If you delete that file without knowing how the relationship between it and the computer works, you could be setting yourself up for trouble. If the computer requests the file and it has been deleted then your computer may come up with an error (this depends on the file).....
Since your problem is solved I don't need to write a fishing bb master thesis on removing problems. I could sit her for an hour trying to write down ALL the possibilities of what is wrong. Don't worry I work with computers all the time. Any questions just contact me.
By the way it might not be a file! It could be a hacker depending on your internet connections, servers, etc. You might want to think about a firewall. These can be both software and hardware. They help keep your system from being infiltrated by hacker and crackers. Hacking programs come free, and are easy to use (From what I have been told). It wouldn't be hard for your son or someone else who knows you ip address to mess with your stuff.
I hope this gives you a little insight into how hard and yet easy things can be. The only true way to fix it is to be sitting in front of the computer. Even then....pull out the battery we're clearing CMOS!
Matt
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Fishing... Not just a sport, not just an obsession, just one strong INSTINCT.