Ok I think window's defender is a virus. Because I remember one like that. You need to look up RKILL program and it will disable it then run a program to kill the virus.
lmfao. I'm sorry, but that was one of the most dumb statements you could blurt out ever.
Yeah, sometimes anti-virus programs disable themselves for no apparent reason.
One possible reason may be because a malware is doing it. I know everybody says that, but
it is a possible thing.
Second thing may be is the fact that those two (Kaspersky & Windows Defender) are in a conflict. So, if you prefer being protected by an antivirus/security software you may have paid for, then leave that enabled, and the other disabled (which in this case, is Windows Defender).
Let me know how it went for you.