My old Viewsonic monitor came with a driver disc, which basically tells windows what refresh rates the monitor can handle.
If you dont have the disc then pop along to there web site and download the drivers.
If you have installed the drivers and they dont work then, have a look to see if there are any newer ones.
Try re-installing the vid card drivers also.
Windows monitor drivers are really annoying. At one point I was able to run my monitor at the supported refresh rate of 150hz...when I installed new drivers windows went crazy on me and I have never been able to get any refresh rate over 85hz.
10-4, thugomatic out
Whether or not you acually see 86 listed as a refresh rate to choose, it can still do it. Usually if you set refresh rate to optimal it will choose a refresh rate that is pretty high, even higher than 86 maybe, depending on your resolution. So try optimal and see if that works out ok.