If none of the leds flash you probably will need serial access.
I think I found the sequence when the LED lights up:
Set your computer’s IP address to 192.168.1.2
Press and hold the Reset button and power the device
. the 3 LED will light up then
. the power LED will light up
. when WAN LED light up release the reset button, power LED and WAN LED will light up, connect the LAN cable and go to http://192.168.1.1

U-Boot 2017.03-armada-17.10.2-gc5a0d2c (Sep 01 2019 - 18:20:09 +0800)

Model: GL.iNet GL-MV1000
       CPU    @ 1000 [MHz]
       L2     @ 800 [MHz]
       TClock @ 200 [MHz]
       DDR    @ 800 [MHz]
DRAM:  1 GiB
U-Boot DT blob at : 000000003f715098
Comphy-0: USB3          5 Gbps    
Comphy-1: PEX0          2.5 Gbps  
Comphy-2: SATA0         6 Gbps    
SATA link 0 timeout.
AHCI 0001.0300 32 slots 1 ports 6 Gbps 0x1 impl SATA mode
flags: ncq led only@pmp fbss pio slum part sxs 
PCIE-0: Link down
MMC:   sdhci@d8000: 0, sdhci@d0000: 1
SF: Detected w25q128fw with page size 256 Bytes, erase size 4 KiB, total 16 MiB
Net:   
Warning: neta@30000 (eth0) using random MAC address - 06:43:50:90:dc:9d
eth0: neta@30000 [PRIME]
Reset button is pressed for:  7 HTTP server is starting at IP: 192.168.1.1
done set host addr 0xa8c0 0x101
HTTP server is ready!