I can't find a "HP pro book g450", only a "HP Probook 450 G4" and a "HP Probook 450 G5".

Anyway, if you still have warranty, let the shop or HP fix it for free. If not, all you can try yourself before having it repaired is the generic reset (disconnect from mains, remove battery, keep power-on switch pressed for 1 minute, put battery in, reboot). If that doesn't help (it's unlikely to do) find a repair shop. Realize that repair might cost more than what the laptop is worth, depending on the age.