acer aspire one nav50 nothing showing on the screen and fan stops after 5 s

I have an Acer aspire nav50 model netbook I was pasting thermal paste on my processor everything was good before this after pasting when I turn it on the first thing is my processor fan stops after five seconds system is still running but the screen is blank too first I thought I damaged my screen connector’s but I checked it by connecting external monitor and the monitor is blank to I clean the ram and tried many things but nothing worked pls help …….