Kossel Problems with ATX/ Heated Bed

Hey everyone i'm having a small issue with my current kossel Mini and any help would be appreciated. I recently Upgraded and added a heated bed! With this upgrade I also am now using a different ATX power supply. The power supply i'm using is rated at 50 amps on the 12v line. I thought this would work fine so i tore it apart and did some work to it. I combined the yellow wires into 3 seperate wire looms and solderd those to about 3 feet of 14g wire each and did the same for the negative side. in total i now have 3 12v positive connections coming from the ATX and 3 ground wires. Then i Connected the Connectors. Soldered on the green Power ON lead to Ground along with the Power OK to ground. I also connected the 2 Orange wires that were already spliced together in the original 24 pin connector on the ATX. (I think it is normally a brown wire but in this case the wires where both a shade of orange)

After doing all this my Kossel powers on fine until I use my heated bed. When using my heated bed the screen will flicker and you can hear the stepper motors turning off for the slightest of a second. it is like the power is ducking out or something. It is only doing the flashing/ or flicker when the heated bed is trying to maintain a temperature or when it is initially turned on. this causes my cossel to loose its home possition during a print and the print will mess up. The Kossel Still Prints ok with the heated bed off just not when it is on.

Any help with this would be greatly appreciated. Below I will attach the links to my upgraded parts along with some pics for reference.

Thermistor im using: [builda3dprinter.eu]
Heated Bed: [builda3dprinter.eu]
ATX Power supply Im using: [EARCH:MAIN_RSLT_PG" target="_blank" rel="nofollow">www.frys.com]