Seasonix psu

Hi ,have been using Seasonic -x 650 Psu ,this psu is the second seasonic x 650 ,the first was replaced under warranty about 18mths ago ,and this one has developed the same issues simply wont boot ! just goes round on endless start/stop/ start cycle ,I have already received the RMA from my supplier ,I replacing the Psu with a 7 yr old Tagan and everything works great,the psu was working on a non overclocked system consisting of asus P5e/intel 8500 core 2 duo 8gb ram and win 7 ,Has anyone come across a problem with seasonic psu ,I notice that the G tee period has gone from 5yrs to 2yrs
any information regarding seasonic Psu would be gratefully received
peter