So your PC suddenly stopped turning on, and you purchased a new PSU in attempt to resolve this issue correct?
As would be normal, check all your power connections and make sure everything on the motherboard, video card, etc is attached to power properly. It's easy to forget or overlook a connector. (such as the 24-pin motherboard power cable, and 4/8pin CPU power connector for some boards).
If everything appears to be plugged in, start troubleshooting individual components. You may need to pull memory out, swap memory chips, see if it boots. Try another video card, etc.
If you can't get the PSU fan to start, video card doesn't actually start, CPU fan doesn't start, there's a good possibility your motherboard itself could have failed.