Computer has no video signal to monitor, motherboard failing?

Hello, my brothers computer was working fine last night but when he went to turn it on this morning. the computer powers on as normal (no beeps) the fans and everything inside looks to be running as they should. the monitor would try searching for dvi and hdmi but after searching it goes to can't find signal. if it's the motherboard failing or dying wouldn't anything attached to the motherboard needing power not be running also?

1. i tried replacing the hdmi cable with another that does work, no good. tried using my dvi cable that my computer uses and also no good.

2. i tried doing both straight to the motherboard instead of gpu in case of it being a gpu issue. no signal with that as well. i tried using my gpu in his build which was no good either.

3. tried making sure no cables were loose, unplugged everything inside and hooked them back up, made sure ram, cpu and gpu were reseated/cleaned up.

4. tried removing the cos battery and putting it back in (didn't try powering the system on without the battery) no good

5. tried unplugging all usb cables, hdmi, power and holding the power on button for 30secs to 1min and plugging everything in again, no good.

side notes: i feel if it's a hardware issue it would be either the motherboard or cpu? my only concern with it being the motherboard is if it were dead or faulty wouldn't there not be power to the case fans, gpu fans/cpu fans, etc? also the usbs have power through them cause his keyboard/mouse led lights are on. if it's the cpu that's dead or faulty i'm not sure how to test if it's that in less i check if my working cpu in my build has the same sockets with his motherboard to test that out, my only worry is if is motherboard is causing issues i don't want to put my cpu in there in the chance of it frying my cpu or anything.

his build is about 2 years old and during the first year there was blue screen issues, black screen issues here and there but for the last year there wasn't any issues anymore.

his build is below

CPU: Intel Core i5-4690K 3.5GHz Quad-Core Processor
CPU Cooler: Noctua NH-D14 65.0 CFM CPU Cooler
Motherboard: ASRock Z97M Pro4 Micro ATX LGA1150 Motherboard
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-2400 Memory
Storage: Crucial MX100 256GB 2.5" Solid State Drive
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive
Video Card: Gigabyte Radeon R9 290 4GB WINDFORCE Video Card
Power Supply: Antec High Current Gamer 620W 80+ Bronze Certified Semi-Modular ATX Power Supply
Optical Drive: Samsung SH-224DB/RSBS DVD/CD Writer

thank you for any help, want to make sure i've tried everything i can to pin point the problem if i need to replace something or spend any money to trouble shoot.