HP wont turn on

i have an hp pavillion a450n and i got comcast internet installed today it the internet wudnt work so the installation guy sed tht i needed to get an ethernet card and install it then it wud work so i bought an ethernet card and installed it then i tryed to turn it on and it wudnt start up at all and in the back of the pc near the powersource a small green light is blinking rapidly and i removed the etherent card and i had the same result. can anyone tell me wat might have happend or wat i cud do to fix it? thnx in advance

 

I moved you to hardware, this isn't a networking issue.

 

thnx man sry im new and dumb lol