Rendering Compatibility...? Is it the monitor?

Ok. guys got a question about rendering and this is not your typical browser compatibility issue. I’ve been a web designer for approx. 8 years and never ran into this problem so I’m hoping someone out there has come across this issue and can help. Thanks in advance by the way!

The problem:
I have designed a website and have done extensive browser testing, OS testing, screen resolution, “the whole 9 yards” so to speak, however today I ran into something very unusual… One of my webpages(there may be more…) actually rendered differently because of the Monitor, not anything else. I used the same OS, same browser, same screen resolution, on another computer, to test my page and it was all jumbled up. Switched monitors, and it looked perfect as it was intended and always had. Switched back to the original monitor(the jumbled one) and low and behold, it was jumbled up… I am completely baffled!!! Has anyone ever encountered this? If so, please share your insight…

The only thing different was the brand of monitor. Both were 17" flat screens, as I repeat myself, everything else was the same. Windows 7, firefox and IE, 6GB, 1440x900 res. Also text-sizing within the browser was properly set, so I’ve ruled that one out. Like I said, I would really like to hear your opinions on the subject. Thanks!

I know this may sound impossible, but it is completely true!

Bizarre – what exactly happened to the design when you changed monitor? The only thing I can think of off the top of my head is that the monitors might have been set to use different DPI settings.

Also, would you be able to take a screenshot from each monitor?

Well, I have a firefox ad that is positioned absolutely in the right hand corner - z-index @ 100. It dropped down about 1/3 of the way and pushed all the div’s below it to the left about halfway across the screen. all the div’s below are at a standard z-index:0 and floated to the left. so the ad should have not affected it in any way. And I can’t make a screenshot because I secretly done it in the office yesterday while I was alone and I’m not sure when I’ll get the opportunity again…LOL. It may have just been a mishap and something wrong with my server. who knows. I’ve also noticed lately that hit n miss, standard links will pop up files from my server asking to download. Could my server be getting ready to crash?

Regarding the download prompt: Is this only happening in Internet Explorer?

Regarding the download prompt: No it has happened in Firefox, IE, and I’ve seen it a couple of times in Opera. Any clues?