First-time user of Pi 3B+ here; just bought from Amazon. I used a new HDMI-to-VGA adapter cable and followed the instructions enclosed in the box, applying power last of all from the official mains unit (nominal 2.5A, 5.1V). The little red light (only) came on but there was no visible activity on the network socket and the monitor stayed on standby. The official microSD card (NOOBS) showed lots of suitable-looking files when I looked into it on my Linux Mint laptop. Power supply issue ? Next actions ?
Did you buy the SD card with NOOBS, or build your own? I got burned a few weeks ago trying to build my first RaspberryPi. Turns out the NOOBS / Raspbian SD card must be formatted as FAT32, which means that card cannot be bigger than 64GB. A larger card will look fine on a PC, but show no activity when plugged into the Raspberry Pi (one steady led on most Pi boards, and no lights at all on a Raspberry Zero computer).
I went thru several SD cards I had laying around (all 128GB or larger) before breaking down and buying a pre-made one. I then bought a smaller card and made a NOOBS installer, and sure enough it worked fine. I then found an obscure article talking about ways to format the 128GB as FAT32 to work with RaspberryPi and put 2 & 2 together!