|Your BIOS password changing may be responsible but it's pretty unrelated to power distribution in your computer. |
First thing to do is check the color of the power button on your computer when you turn it on. If it's anything other than solid green, chances are something is wrong with either your power input (ac adapter or battery) or the power distribution (motherboard). A solid green power button is how it's supposed to be when turned on correctly. If it's not solid green, find another computer and google your computer manufacturer and model and the color of your power button, you should find a link to the manual that will tell you what's wrong with the power and what exactly you need to replace.
Assuming your power button is solid green as usual, you can rule out power issues and (if you have it) attach an external monitor to your laptop and see if you get an image on it. If you do, you need to replace the monitor on your laptop. DO NOT ATTEMPT TO DO THIS YOURSELF UNLESS YOU 100% KNOW HOW. The wires are extremely small and easily breakable, and worst case scenario you break the monitor and the LCD crystals spill out - these cannot be replaced with anything sold in a retail store - and worse yet they are made with chemicals that may have a reaction with your skin if you get it on your hands.
If you don't get an image on your external monitor, you'll have to replace your graphics card or motherboard if your graphics card is integrated onto the motherboard. Better to just replace the laptop in that case as you can buy a new laptop for the same price as a motherboard assuming you aren't purchasing a fancy gaming laptop.
Other things you could try for free: Try a different wall jack. In rare circumstances your wall jack isn't getting sufficient power to your laptop if it's plugged in - and if it's a problem with your wall jack then call your electricity provider and have them take a look at the wall jack (or you may have to call an electrician). The power grid in 1st world countries is pretty stable compared to the rest of the world, but even so it has flaws sometimes. Also, try a different electrical appliance in that wall jack. If your laptop is plugged into a UPS or surge protector, try plugging it directly into the wall and see if that makes a difference. If it powers on, you'll have to replace the UPS or surge protector. If you're using an ac adapter other than the one that came with the computer, double check the wattage on it and check with the manufacturer to make sure the wattage requirements for the computer and the wattage of the ac adapter match up.
If you can rule out issues with the graphics card, try an alternative ac adapter if you've got it - also make sure you power on the laptop with just battery and just ac adapter, not both in the system together as you normally would. If you don't have spares of either, I would recommend buying a 2nd ac adapter to try first since that will be both cheaper and easier to obtain.
Check with your manufacturer to make sure these parts are under warranty, you could get both for free if they are. Batteries are known to have a short life, though, so most batteries won't be covered even under the system's extended warranty.
Hope that helps.
message edited by techninja