The first question I'd ask is if it makes any startup chime(s), and if so, what. If it's making anything other than the single "bong", then it's indicating a hardware failure. If it's not making any sounds at all, but lights indicate it has power, then an SMU reset might work, rather than the PRAM reset. SMU reset varies by model, so you'll need to look up the procedure for that model.
Good suggestion! Note that one needs to open the case to gain access to SMU reset button it's not like PRAM reset.