300 watts was never enough for my Toshiba, it was always hot, and eventually burned out, I now have a 600 watt inverter, and have laptop, external screen, external hard drive, a printer (sometimes) and phone charger running off it and it stays cool. I have changed to a Dell lap top now though.
Heat is the enemy of any electical device, so if yours is hot it is struggling to do the job and will give up long before a cool inverter.