Ok if you can't load the os then it is hardware,please correct me if I am wrong but we know it is not,
1 The hdd because you tried another
2 You tried a known working cdr drive
3 Replaced cables
4 Have no cards installed
5 Have installed a new psu
6 Temps are good
Now try running memtest86 to test the ram, if there is more than 1 stick test each stick individually and let memtest run for atleast 3 passes on each.
Make sure the 4 pin 12v connector from the psu the the mobo is connected
Clear the cmos and load the defaults then check that the cpu/fsb is correct also check that the dram clock is set at the same speed as the cpu.
Check for correct vcore voltage.
Post your system specs mobo, cpu, ram, psu or the brand name of computer with model name and model number.