Graphics NF7-S2 AGP Aperature Problem

Just a few days ago I built a computer for someone. I gave it an Abit NF7-S2 motherboard and ATI 9800 Pro 256MB graphics card. For some odd reason, when I change the AGP aperature to 256MB in the bios, the computer refuses to start up after I save and exit from the BIOS. The computer doesn't display anything and beeps (I don't know the exact number of seconds). I have searched on the forums for this problem and found the same thing has happened to someone else, however, it didn't happen as a result of a change in the AGP aperature. Does anyone know any way to fix this problem?

 

erm, don't set the aperture to 256MB?

it *really* doesn't need to be that high. set it to 64, or 128. remember, the aperture is the amount of system RAM reserved for use by the vid card when running out of its own memory. the 9800pro you're using has 256MB memory. do you HONESTLY think it'll have a big problem with needing a big aperture?

*edit*: looky here:
http://www.ocfaq.com/article.php/overclocking/vidcard/43

 

Oh, I didn't realize that that's what it is...

Well, thank you.