Problem with either Asrock Motherboard or ram!

SO i bought a new motherboard yesterday,its Asrock B75m. Good board with good specs and up-to-date and all. Ram i have is 2x2GB Dominator DDR3 Corsair,timings are 8-8-8-24.
Problem is,yesterday and even today,whenever i turn it off,sometimes it doesnt start and sometimes it doesnt starts AT ALL! I mean the fans spin for a few seconds and i can hear the HDD drive and see DVD rom lights but then everything turns back off again. Yesterday when i put everything in for the first time,it did the same thing about....more then 10 or 15 i guess. Its completely random. Then i turn off the power and then again turn it again and after a few tries it works.
I mean there is absolutely no pattern to this. I know the motherboard is fine,and so is the ram....probably..i just want to know what this problem is related too. Ive tried to run memtest86 from my USB and i had no idea what to do si im now going to read a tutorial or something and try again.
Any help in the meantime is appreciated :)

i3 2100
Asrock B75m
Corsair Dominator 2x2GB
GTX 460 SC
HDD Seagate
And a Samsung DVD RW
Also finished with memtest86,first pass gave 0 errors,second one gave 217 No wonder it was cheap. WIll be buying Corsair XMS3 2x2GB in a few hours. And can anyone tell me for sure that the 217 errors memtest gave were from the Rams? or could they be from somehwere else??

Its boots sometimes and sometimes it doesnt. And How is this ram: CORSAIR VENGEANCE LOW DDR3 4GB-1600 2GX2 (CML4GX3M2A1600C9)
Is there a big difference b/w low profile and normal ram? Its for the same price as MXS3!

You should run MemTest on EVERY stick of RAM, by itself, to see if you can isolate the bad stick of RAM. Once you weed out the culprit, try running the computer on the remaining RAM. If it works right and boots up many, many times with no problem, you know you have exactly ONE(1) stick of bad RAM.

As for the RAM you mentioned.....do you NEED the low profile kit? If not, the regular Vengeance will work just fine.

no i dont NEED the low profile kit,i dont even know whats the difference b/w the normal and low profile rams.Its just that in the same price range,Vengence low profile and XMS3 2x2GB are available and in the same price range, Vengence 4GB and Gskill 4GB both single modules are available. I Want to know which would be the better choice.
I.E:
CORSAIR XMS3 DDR3 4GB-1600BUS 2Gx2 (CMX4GX3M2A1600C9)
OR
CORSAIR VENGEANCE LOW DDR3 4GB-1600 2GX2 (CML4GX3M2A1600C9)

CORSAIR VENGEANCE DDR3 4GB-1600 4GX1 (CMZ4GX3M1A1600C9)
OR
G.SKILL Ripjaws Series 4GB (1 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)

Dont know how to check and compare timings in bios but i think they are the same since only 8-8-8-24 is visible.
And when i said i dont "need",i meant it in a different meaning :)
Anyways its obvious there is a problem with my current ram. And i AM going to buy new ones just need to know which ones from hte mentioned in the above post.

I know this is a really old post... Just hoping to help others that read it....
I am having the same issues with the same board. I just got the board this morning for a new build I am doing for my girlfriend. I read this thread and then found many threads with the same problem. Those that figured it out posted that the ASRock board has bent pins in the CPU socket. In all the posts I found, the bent pins were always pins associated with the memory slots. I took out my CPU and inspected the board and sure enough I found the same pins bent. I have built countless PC's over the years and have never damaged a motherboard. Because of the amount of posts with this problem I have found... It appears to be a problem with ASRock's board. I found two posts where people looked at the board before installing the CPU and the pins were bent. I have a new board on the way to me.
Take out all your ram and see if the PC turns on and stays on..... Mine did, I then tried each individual ram slot and only number 3 worked every time and the PC would boot.
Also, I tested all ram in another PC and it is fine. Also each stick works in slot 3 with no problem.