I'm having the weirdest issue. Been trying to transplant a PC into a new Antec case from an Optiplex 7010 DT but with mostly different parts. I've kept the CPU, an i5 3470, the HDD and the RAM, but got a different PSU (Riotoro Onyx 750w, very good according to reviews), motherboard and GPU.
At first I attempted this with the original Dell motherboard but all its proprietary connectors caused problems, then I tried to workaround the power cable connector and pretty much ended up breaking it and got a cheap Gigabyte H61 instead. With this I put everything together and turned the PC on and the case RGB lighting pulses red, there's no display to the monitor and the CPU fan stops and starts every 10 seconds or so. This is odd, first of all I'm not sure why the case fans do that, do they normally pulse red if something is wrong? Weird, maybe it's a coincidence. Well, I went through the following steps to try to diagnose:
-Remove GPU and try motherboard video out instead
-Remove and reseat RAM in different configurations
-Remove RAM altogether
-Try different RAM
-Remove CMOS battery
-Clear CMOS with jumper
-Remove all additional fans, SATA drives etc
-Try different CPU - a working Pentium I had lying around
-Try different PSU - plugged in necessary power cables from a working ITX PSU I had lying around
Nothing worked! Just exactly the same problem again. So I guessed that it surely must be the motherboard at this point. I bought a new one, this time an Asus P8H61 and basically went over all the same steps again, with no luck. Then I bought ANOTHER motherboard, this time an Asus Z68, and it's taken another turn. Now, the CPU LED flashes for half a second and spins the fans, it turns off and starts again infinitely.
Surely someone must have some idea somewhere please?