Vista - big display problem; can't get native resolution anymore!

hey guys, been wrestling w/ this for a week & a half now, & can't figure it out for the life of me...

have a gateway FPD2185W 21" WS monitor and an EVGA 7300GS. have been using 'em w/ vista x64 for 4 months w/ no problems (RGB; the dvi port on the crappy Gateway blew last winter).
was using my box normally, hadn't updated any drivers or installed any new apps in a while, when the screen just flickered and kicked me into an 800x600 resolution. when i tried to change it back to the monitor's native resolution (1680x1050), i found that it wasn't available anymore... the best resolution i could get was 1600x1200. when i 'check all modes', nothing above 1600x1200 is listed.
I've tried restoring to an old save point, i've tried uninstalling and re-installing 3 diff versions of the forceware drivers (incl. the most recent), i've swapped in my old x600 card & installed the latest catalyst drivers. NOTHING WORKS!!! When i plug the monitor into my old computer tho, f*ckin' bob's yer uncle... no problems whatsoever.
WHAT THE 'EFF!!!
Please someone tell me you have a solution! My eyes really hurt from looking at this fuzzy, non-native resolution!!!

It would seem the graphics card and monitor aren't getting along for some reason.

Check the Monitor Driversand at the monitor in the Device Manager. Try the monitor on your integrated graphics output. This should tell you if it is a software issue (If it works fine).

Also look at the BIOS PCI-e settings and see if there is anything there that could cause the problem.

While you're at it, check your monitor panel settings (menu within monitor itself)

Good look.

problem could be on your motherboard in the northbridge - suggest clear the BIOS - usually a jumper near the battery

also check device manager if you havent already

i've been using same monitor for a while - no problems to report - luck of the draw i guess

cheers,
simon