[Solved] Bad memory slots?

Im fairly new to building PCs, this was only my third, but ive never had this happen to me before... After putting everything together (half new stuff from newegg, half taken from an old PC), I went to power on the PC and the screen just stayed black. After playing with a few other things, I removed two of my 2gb sticks and only left one in, and the PC booted right up.

So thinking it was bad memory sticks I tried each stick in the first slot, and all 3 sticks worked, but replacing any memory in either of the other tri channel slots and it stops booting. I tried putting two sticks in the second tri channel set of slots, with one stick in the first set, and while the computer booted, it only recognized the one stick.

So my question is, is it definitely a motherboard with bad memory slots, or am I still missing something?

Specs:
ASRock X58 Extreme LGA 1366 Intel X58 ATX Intel Motherboard - Retail

CORSAIR DOMINATOR 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Triple Channel Kit Desktop Memory Model TR3X6G1600C8D - Retail

XFX HD-587A-ZND9 Radeon HD 5870 (Cypress XT) 1GB XXX Edition 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported ... - Retail

Intel core i7 920 2.67ghz

... all new

Rosewill 550w psu that i ripped from my old pc

Ya, that was the first thing I did, I mentioned it at the start of the second paragraph. All 3 sticks worked in the one slot, computer booted perfectly.

Ya, I figured, just wanted to make sure before I go through the RMA process... serves me right for spending the money on other parts and skimping on the mobo. Thanks for the reply.

Best answer selected by Guaritor.