2 years ago I bought a new Dell Intel® Core™ i7-5550U with uBuntu. And I still have a warranty but there are holidays in my country so I can go to a pc expert for about next 10 days. Also, 8 months ago they replaced my keyboard, graphic card (Nvidia GeForce 920M) and hard drive. I didn't drop anything on my keyboard or try to damage it.

Few days ago random keys started randomly stop working. Sometimes they don't work just for a few seconds but other times they don't work up to 30-60 seconds or even more and then they work again. it happens when I'm using the keyboard for some time. I'm sure for next keys: QWERUIOPM (they happen to stop working all the time) and many others but I'm not sure which ones, sometimes TKY and others (not the English keyboard so Y and Z are switched). And the left CTRL is not working in general. Ctrl stopped working about a week or two later after I got my laptop back from a pc expert (8 months ago) but I didn't took it back because I didn't wanna be with no laptop for another 14 days.

I can't open laptop because of warranty. I've tried to clean keyboard with a brush but there was nothing under keys (keyboard still looks like a new one) and it didn't fix anything. At first I've also used a system restore for a few days back before the problem appear but it didn't fixed it so then I've deleted (formatted) everything from laptop and made a clean installation of Windows 10 pro from usb but that also didn't fixed the problem.

I'm writing an essay and it's very annoying because this problem is taking me much longer to do my work and I'm gonna be short on time because now I have to wait a week till holidays are over and another 14 days or more so a pc expert fixes the problem.

I wonder if anyone knows what the problem could be and if there is the way I could fix it by myself?
I haven't tried with another keyboard yet because I don't have one with usb but I'm buying it online right now. I hope it will work.

Thanks in advance!