“Will not start” can mean no sign of power, lights or fans but no picture, or a screen that stops before Windows loads. The safest next step depends on which of those things is actually happening.
Look from the outside first
Say whether nothing happens, it briefly starts and stops, or it remains powered on.
Note only what you can safely observe: power lights, fan movement, beeps, clicks or an unusual smell.
A completely black screen, a logo, an exact error or a recovery screen are different symptoms.
A clear photo of the screen or visible indicator lights may be useful. Keep passwords, recovery keys and personal information out of it.
If safe external checks cannot separate a power problem from a display, storage or other hardware problem, helpmypc.ai should say so and help you consider Repair instead of leading you through deep hardware work.
Ask helpmypc.ai
Start with the symptom. helpmypc.ai will ask for the useful evidence it needs before suggesting a cause or a next step.
Get help with a computer that will not start