You say you use a tv as a monitor? .... ps if the mouse and keyboard turn on means that the machine is working ... ps connect it to a pc monitor find out if it turns on or presents the same fault .... greetings
Ps rule out with another hard drive if not already the problem must be on the board or processor ... greetings
I suggest you disconnect everything taking into account to take pictures of the connectors to guide you when assembling ... ps clean the entire board even take out the processor very carefully and when placing it taking into account its position this placing new thermal whore. Clean the soket with an equal brush the entire plate ... connect .. comment .. luck ...