I'm running Fedora Core on a Dell 2400 with a Daytek DT-95P monitor. After some messing around, I managed to get different resolutions working, but I can't seem to change the refresh rate. Preferences > Screen Resolution and xrandr both report 85hz but my monitor (and my eyes) say 60hz. I even tried adding Modeline's generated with videogen to my XF86Config but it didn't help. My monitor specs are setup.

Any suggestions? Thanks!

Hi!
I don't know if this helps, it's just an idea
I've observed that some distros use the file called "XF86Config" and others use "XF86Config-4" in order to configure the X server; are you sure that Fedora uses "XF86Config"? Couldn't it be "XF86Config-4"? (I never used Fedora; is just a guess)
Regards

I don't seem to have a XF86Config-4, although reading the docs, it sounds like it looks for this name first, and then for plain XF86Config. So I don't think that's the problem. And my changes do have an effect, so presumably it's the right file.

The XFree86.0.log contains the following error:

Extended Bios function 0x5f05 not supported
Failed to set refresh rate to 85hz

Does this give anyone any clues?

Also having problems with changing monitor refresh rates.
Tried modelines from XF86Config-4, but couldn't find any help from those.
At the moment I have 1280x1024@85hz, and I would like to get 100hz, because it's more pleasant to play games with.
I have Samsung 959NF and Radeon 9800Pro.

I'm not sure what the error means, but I have always had trouble manually editing XF86Config. On my Debian machine I booted a Knoppix CD and copied the resulting XF86Config-4 file to use. Since Knoppix magically auto-configures everything, it works great. Knoppix probably won't work for a Red Hat machine, but you may try booting a MandrakeMove live CD and see if it works at 85hz. If so, you could copy the XF86Config-4 file and it should work since Mandrake is based on Red Hat. It is an un-educated solution, but may be a quick way to get things working.