Ps4 pro turns on almost everytime with difficult

So I buy a used Ps4 pro , the seller said that the console was going off when he tries playing certain games online . I on the console and inserted Fifa 18 , it was loading then went off .. I retried with other CDs some it went off(loud noise ) achowing signs of overheating , some it didn’t , so I opened the console , I realised console had been opened , I saw a tape around the connector cord between the mother board and the power supply .. it was a bit rough so I took it off .. I got to where the main board and realised there was no thermal paste , which i did replace .. i then reassembled everything Ps4 pro was working perfect , kept it on for about 5 hours and over it was good. the following day I tried turning it on ,, it wasnt responding .. I changed positions , turning turning the console around , then it worked .. it turns on almost every single day but need to change positions or tap it before .. it never goes off when it on until i turn it off ..

my question is : where do u think the problem is , the cord ? Or something else .

sorry for the long message .. please try and assist me if you can or have any ideas..

thanks so much in advance