My iMac(Mid 2007) won't turn on

I have an iMac from Mid 2007, that will not respond to the power button. I have tried reseting the SMC, reseting the NVRAM, removing and inserting RAM, trying different power outlets, and waiting a few hours to turn it in. There is no signs of life from the computer, no fans on, HDD not spinning, DVD drive not making the sound it usually does when you power up the computer. The hard disk which is a Seagate 1TB HDD, which was installed in 2011 has a S.M.A.R.T status of Failed. This iMac has had to been repaired 4 times by Apple, and it is out of warranty. The memory is 4GB Kingston RAM 2x2GB. It was working until

I powered it off normally, and has not been used since September 2013. I'm assuming the PSU is dead, because it is not responding to the power button. Thanks for any helpful suggestions...