Power supply blue light switches off when I plug it into the laptop.
I have an Alienware 17 R3 and recently updated the BIOS and the other day I noticed the “annoying” blue ring on the charger switched off, to get it to come back on I need to disconnect from the laptop and switch off and on again. But several times since it will stay illuminated until I plug it in, the laptop hasn’t moved from my desk and the power pack has been under the desk so the only thing I think that could of damaged it would be this update.
It had a replacement motherboard a few months after purchase but now a few months out of warranty, is it only the power supply or worse?
If that doesn't solve the problem, the mainboard is bad -- Dell's warranty on replacement parts is 90 days. If it's been less time than that, have the board replaced again. If you had it replaced elsewhere, contact the repair shop to find out what warranty they offer on the repair they did.