All anti virus programs that I know of turn off Defender when they are installed. Example: When you install MSE it will turn off Defender as it should. I would suggest at least to start off would be to remove all anti virus programs and installing MSE.
Microsoft Security Essentials - Microsoft Windows
As I have mentioned before it will turn off Defender because it is not needed. It wasn't worth much in the first place. Check and make sure the built in Windows 7 Firewall is running. No other Firewall installed.
Remember that you should only have one Anti Virus and one Firewall installed on your computer at one time. Feel free to ask any other question and let us know how thing are working out for you.
My Computer
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Home made Desktop
OS
Windows 10 Pro. 64/ version 1709 Windows 7 Pro/64
CPU
Intel i7-6800K @ 4.3
Motherboard
ASUS X-99 Deluxe II
Memory
Corsair Platinum 16 gig @2400
Graphics Card(s)
EVGA GTX 1070 OC
Monitor(s) Displays
Asus 27" LED LCD/VE278Q
Screen Resolution
1920-1080 or 1280-720 HDMI
Hard Drives
INTEL SSD 730-240 Gb Sata 3.0/
PSU
EVGA Platium 1200W
Case
Phanteks Luxe Tempered Glass 8 fans/ one radiator
Cooling
XSPC/ Water Cooled CPU
Keyboard
Das 4 Professional
Mouse
Logitech M705/MX Anywhere 2-S
Internet Speed
100 mbits
Antivirus
Microsoft Security Essentials/ Malwarebytes Premium 3.0/ SAS
Browser
I.E. 11 default/Firefox/ ISP Time Warner Cable/Spectrum
Other Info
LG BluRay Burner/
Sound system-KLipsch-THX/
Icy Dock ssd Hot Swap bays.