Ah this happened to me just recently my first hatch also. I have a still air hovabator with auto turner. On day 25 i still had just like you no pips, peeps ... zilch nothing. I candled them most still alive! I opened one that i thought was dead ooops it wasn't but it was shrink wrapped. ANother i opened was dead but fully formed, some others oseemed small for dates. Day 26 i did the wrong thing and opened up the last two, one i broke the membrane - big mistake!!!!! The other I just chipped into the air cell - it died that day anyway. It so heartwrenching and stressfull i swear i was becoming depressed over it.
I was running my still air incubator at 100 with many fluctuations. I'm now into day 9 of my 2nd attempt. Got another (expensive) thermometer which shows my mercury one to be only 1/2 degree warmer. Which means i was running it at 99.5. This time i have upped my temp to 101.5. At night it drops down to 100.5 and towards the end of the day it is 101.7. Looking at the troubleshooting chart, it seems that i was yes running it too low. As lower temperatures delay/slow chick growth, which explains why day 25 and no hatch!
I'm a bit confused with humidity though? How are you going with it? I am following manufacturers instructions, 1 tray filled, vents closed and humidity is about 55%. Will opening a vent bring it down a bit? Because everyone seems to run their humidity at 35%.?
Anyway, when i read your post i thought it was mine from a couple of weeks ago, you sound just like me.
Goodluck, one thing is though i wished i hadn't of touched them/opened them on days 25 & 26. I have to live with the thought that they may have eventually hatched. I read a recent post yesterday that someone's hatched on day 27 i think.
Let us know what happens.