We upgraded to w10 long ago and it was fine.
To force the k55n to not load an OS I would remove the HDD. That way I can be sure nothing of W10 is in play on the laptop.
If you get no display anywhere then it may be an unfortunate coincedence that the laptop failed in some way during or after the upgrade. Our K55N's are from 2012 and one is dead now but from a glass of water. The other is fine.
-> The one with the now bad motherboard does power up, fans go, the DVD drive does a seek but it is really dead.
Given the age you could have many issues but here's what I would try.
1. Remove the HDD so no W10 is in play.
2. Try to get to the BIOS.
3. If you make it to the BIOS disable any Fast Startup item you find then save and power off and put the HDD back in.
4. Use a Volt meter on the CMOS battery. It looks to be the usual CR2032 so you want 3.0V or a bit more there. If you are not a PC tech or such, try a new battery (here, we get them for under 1 buck.)
5. Read https://www.google.com/search?q=k55a+cmos+battery and this link:
So there are a few things to try before you call it dead and back to repair.
I'm not sure if this is correct category for this question - feel free to move it if it isn't.
I have reinstalled Windows 10 on my laptop, as it was getting a bit slow. I formatted all of the disks before reinstalling it from USB. After reinstall it worked fine, I connected it to the Internet, transferred under a 100GB of my files from external hard drive, started installing software (Foxit Reader, Dropbox, Google Chrome, Skype and the like), updated my video card driver from a file downloaded from Intel website, as well as Free Driver Scout which updated my other drivers. It connected to the Internet and everything was working well. After installing all these drivers and software, I decided to restart it.
After restarting it, it loaded up saying it was unable to Boot from USB. I thought there was an issue with the BIOS setting so I restarted it, tried to mess around, but I ended up restoring default settings. After that, whenever I turn on my laptop it starts working, I can hear it working and trying load CD-ROM, the ventilation is working, it is charging and the lights that show that it started are on. Besides that, I can't do absolutely nothing - it seems to be working, but the screen is dark and the Windows won't boot. I can't go into BIOS as well.
I tried taking the battery in and out, as well as attaching an external monitor. I don't know what else to try, as it won't even go into BIOS. Please advise on things to try that might get it working. Let me know if you need any kind of additional information and I will do my best to provide it.
Intel HD 4000