I got an old phone: an HTC WildFire S. Everything works fine, except that the power button has gone bad. Can I start the phone from my computer over a USB connection somehow?
Many PCs can be woken from sleep mode via a keypress. Some, if configured to allow "wake on LAN", can even be woken via a specially-composed Ethernet packet.
I'm unaware of any way to force an Android device to power on using a special USB command.
You can try removing and reinstalling the battery.
Or you can try connecting the phone to a charger; there might be a slim chance that this will force it to power on.
If that doesn't work, you can try a Google search for [ how to power up Android phone without power button ]. You'll find lots of results, including an article on the AddictiveTips website and many others. These articles have additional suggestions which I haven't mentioned. Maybe one of the articles has a tip which can help you.
If none of the aforementioned ideas help, you can then either:
most of flash tools have a "reboot after flash" option. here is example for Mediatek devices
while in fastboot mode type in cmd.exe
fastboot oem off-mode-charge 0
this works similar for flashing stock rom (tools without readback option). for samsung devices (no fastboot) a JIG dongle may help
When your phone is not turned on it can't have a adb service running (Disregarding the possible technical difficulties it would also be a security issue.)
Try the following instead:
Your device should boot now. I'm not sure if this will work for you but i booted my old ZTE Blade using these steps.