Ladies and gentlemen, I found a solution
The problem was: My stupidity
The whole problem was that I had an empty SD-card adapter (without a micro-SD card plugged inside it).
I know it caused some havoc in windows when I accidentally opened the SD reader, but, as I found out yesterday, it also caused the boot lag.
I removed it, windows booted up in seconds. I put it back, and it was slow agian. I repeated a few times, and I can tell for sure that it's the empty card adapter
Thank you all for your suggestions and for trying to help me, and I also apologize.
Oh well, I learned a new thing or two, one of them being 'do not keep an empty SD-card adapter in your card slot'