Question No signal after switching case?

[sampletext_xyz]

So basically I came over to a friends house to help him with his new case and Hydro X water cooling. We didn´t manage to get the water cooling done yet, but we got his old PC into the new case. (We didn´t upgrade anything except for the fans. Other than that, same specs as before).
But after turning on the PC, all of the fans all turned on, but there was no signal on his monitor. After resetting a couple of times, we noticed that his GPU fan only started spinning for like 1s before stopping. (It is an MSI GPU and I´ve read that they apparently only turn on their fans if they really need to, so I assumed that it´s working fine).
The CPU fan is on, the case fans are spinning and glowing, but there is no signal coming out of it.
The GPU is also connected via a riser cable on the HYTE Y60, but we tested it on the mainboard directly, and still got no signal.

Also, the EZ boot LED lights up, which according to MSI, "indicates booting device is not detected or fail."
So I assumed that my hard drive may not be recognised?

Specs:
AMD Ryzen 5 3500 (no integrated graphics, so we cant check for a broken gpu)
MSI RTX 2070 super
16gb DDR4 ram (supported by motherboard)
1000W PSU, so enough to power up everything
B450M PRO-VDH MAX

As I said, the PC worked perfectly fine before, and now it just refuses to give a signal...
We´ve tried everything. CMOS reset with battery and with a jumper; only using one ram stick; etc.
Could there be a much bigger problem, such as a broken CPU or even the GPU? Or even a mobo problem?
Are there any other things i can test?

 

[Ralston18]

Regarding that 1000 Watt PSU: make, model, condition (new, refurbished, used), source?

Also:

"The CPU fan is on, the case fans are spinning and glowing, but there is no signal coming out of it. "

Explain: what is "it"?

And, without the cooling being installed consider that some CPU thermal shutdown is occurring.