"Won't turn on" actually covers three different situations, and each one points somewhere else. Nothing happens at all. Something happens but nothing shows on screen. Or it starts, then shuts itself back off. Which one you've got matters more than almost anything else you could tell us.
Completely dead: no lights, no fan, no sound
This is almost always power, not the laptop itself. The charger has failed, the cable has a break in it, the port isn't making contact, or the battery has dropped so low it won't wake up on its own.
Lights and fan running, but nothing on screen
The laptop is receiving power and starting up, so this isn't a charging problem. It's either the screen itself, see our screen replacement page for the external monitor test that tells the two apart, or a fault further back on the motherboard that stops it from posting at all.
Turns on, then shuts off again
Usually one of two things. A battery that's failing badly enough that it can't sustain the load even briefly, or overheating protection kicking in and shutting the machine down before it damages itself. If it happens within seconds of powering on, before it's had time to warm up, that points more toward the battery or power delivery than heat.
How we work it out
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Rule out the charger
Test with a known-good charger and cable before opening anything.
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Check the battery
Run from mains power alone to see if the fault follows the battery.
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Listen and look
Beep codes, LED patterns, and fan behaviour all narrow it down fast.
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Open it up if needed
Only once the cheap causes are ruled out, so you're not paying to diagnose the obvious.
Common questions
I plugged it in overnight and it still won't turn on. Is the battery dead?
Maybe, but it could also be the charger, the cable, or the charging port itself not passing power through to the battery. That's why the two checks above matter before assuming it's the battery specifically.
It turns on but gets stuck on the logo screen. Is that the same problem?
No, that's a different fault, usually a drive or Windows problem rather than a power problem. It still counts as "won't turn on" to most people, so mention it when you call and we'll point you the right way.
Could I have damaged it by leaving it plugged in?
No. Modern laptops are designed to sit on charge indefinitely without harm. If anything failed, leaving it plugged in didn't cause it.
How much does it cost to find out what's wrong?
The phone diagnosis is free. Tell us what happens, or doesn't happen, when you press the power button, and we'll usually narrow it down before you book anything.