still don't hear anything. Did you pull the clutch cover? When you move the shifter the linkage should turn the shifting drum, if it turns the drum and it doesn't go into gear then there's an issue with the shift forks or gears, split the cases. If when you move the shift lever the linkage doesn't engage the drum, or move it correctly then it's probably worn out and needs replacement, easy fix. Try turning the shifting drum by hand and see if it goes into gear.
do you have a service manual? If not, stop and get one before proceeding.
you can download one here:
https://www.tradebit.com/filesharing.php/search/0/cr80rfor $5.00 but search around I got lucky and found the original factory service manual for Kyle's KLX450R on line for free. I downloaded it and printed it out and put it in a binder.