About 6 months ago I built a desktop system.
Case: Rosewill Challenger
PSU: Antec 550BP
RAM: 2X4GB Corsair DDR3 1600 (PC3 12800) MOBO: Gigabyte GA-Z68XP-UD3
CPU: INTEL i5-2400 3.1G
HDD1: 500 GB Seagate Barracuda
HDD2: 160 GB Western Digital Caviar blue
Video Card: Radeon HD 6670 1GB DDR3
Run well without any issues or problems and did everything I wanted. Now it has suddenly developed an issue where when I start up the PC will come on for about 2-5 aeconds. Just long enough to get the fans spinning. It then powers down. It will automatically restart, run for about 30-45 seconds and then power down. It then repeats this cycle until I switch off the PSU.
For troubleshooting, I went through and disconnected the harddrives, removed one RAM module, and video card. Same results, I then reset the CMOS by removing the battery for several minutes.
Following this I had the PSU replaced by Antec, I put the replacement PSU and made up all my connections. i then booted up the PC and everything worked perfectly. Several days later when I tried to start the PC the reverted back to its old problems.
I am running out of ideas to try.