Do you have apps that come with the laptop (that may tweak your hdmi output)? You may want to uninstall those programs.

I used to have an energy saving app from lenovo, and it messed up my gpu completely in windows 10. Once in uninstalled it, the laptop's back to normal.

So weird to see so many complaints abt win 10. My experience with it has been very smooth.

So wait you have obvious driver issues and somehow it's the OS fault if the constructor decides not to maintain their driver on older hardware???

Sure if doesn't work 7 is better obviously but on compatible hardware win10 is far better in performance and stability by all measurements... And probably more secure

I've got no issues with windows 10 HDMI on my laptop. I actually love Windows 10, it's pretty good. And I hated 8. I think it's simple and back to the basics with a minimalist flair. I'm even starting to like it more than 7. It should be noted I've got a pretty beefy Nvidia graphics card, 32gigs ram and a i7 processor so maybe that's why I'm not experiencing any lag on my machine.(desktop). My laptop also doesn't experience lag but once again, it's pretty beefy. Maybe try upgrading your machine or downgrading back to windows 7 or 8.

When did you install windows 10? If it has only been a month, there should be an option to downgrade back to the previous OS. Usually takes about 5 minutes to revert back (at least for me it did)

If you can't do that, burn a windows 7 image on a dvdr or dvdrw, and if you need an activation code...um...google is your bestest friend. 

i've searched for a decent time. Seems as though all i can find are scam websites.

I'll send you a PM.

Windows 8.1 along with Classic Shell Start Menu extension works great.
I believe there is a "roll back" to revert to previous OS version which may still be saved on your drive somewhere.
If you had an "installer partition" on your drive, that could still have the original OS version ready to install fresh.
Did you not make installer/boot disks/USB? Even if not, the computer came with licence for 8.1.
So you should be able to contact HP and they will send you new install media or otherwise help you.

Yeah, you could do this too, it's probably the most legal and authentic way of doing this other than buying it.

Disabling the Bitdefender firewall and enabling the Windows Firewall got rid of all random lags, freezes, crashes and driver issues and turned Windows 10 from the crappiest OS I ever used to the fastest one on all 5 PCs in my household. If you use any 3rd party firewall, it's worth checking this.

Windows 7 is ok, has crap memory management though. (Might be in all windows versions)

I occasionally have to revive my wife's win 7 laptop when it has ground to a halt again. It has 8gb of ram, if that gets full windows gets very moody. For some reason it insists of utilizing the hdd at 100%, organizing the swap file I guess, taking all available system resources to do so. For example when she was organizing pictures she left the used the windows photo viewer to check them, didn't close them, windows opens a new one every time. For some reason Windows tries to keep them all active, when she reached about 90 of them the laptop was unuseable. Impossible to operate. Bringing up the task manager to find out what was going on took almost a minute. After closing down all the offending photo viewer windows it still took more then 10 minutes for windows to release the memory and stop working on that swap file.
(She manages to grind her iPhone to a halt too though :)

I got used to windows 8.1 on my laptop. I still regularly close and re-open firefox to clean up memory as it will also grind to a halt over time. Sometimes it still gets unresponsive, disk usage 100%, track it down, usually it's downloading a windows update or doing some other unnecessary background task. Why is Windows always about Windows first, user last. I have 16GB of ram, no need to kill my hdd while downloading an update.