HD 6870 with CM elite power 460w?

A 500 watt PSU is really recommended for that card, but you might be able to pull it off with some creative cabling.

help me with the creative cabling thing...    

Your power supply has (I assume) 1 pcie power connector for the video card, but the video card requires two power connections. The idea is that you use two molex connections to make a second PCIE power connection for the video card.
You need an adapter like the one pictured here:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

NO! "Creative cabling" only works if the PSU is able to handle the intended load. I would not trust a liar-labeled Crappermaster for your HD6870. It may work, for a while (especially if you're gaming, not stress-testing), but it may smoke too. Fortunately, that IS one of the few low-end Crappermaster units that HardwareSecrets found to actually possess working protection circuits. The point remains though, all the creative cabling in the world won't make up for insufficient capacity.

ok......by the way i knew that i'd have to use the Molex pin connector....and yeah i'll only intent to game at a resolution of 1366x768 (please dont tell me to not buy hd 6870 for a resolution of 1366x768 and to buy a hd 6770 or sumthing else.....i will upgrade to a new 24' monitor soon) and i will be playing BF3,Crysis 2,GTA 4 (and upcomming GTA 5 ),NFS RUN,Skyrim 5 ,Batman:Arkhym City .....and all the future games......so no stress testing playing at 1366x768 wouldn't stress my card i suppose(i think it will use max 60-70% of card).....and i will be upgrading to a corsair gs600 after 4-5 months or equivalent.....  

Cooler Master Elite Power 400 W Power Supply +12V rail distribution:

• +12V1 (solid yellow wire): ATX12V/EPS12V cable, peripheral connectors and SATA power connectors.

• +12V2 (yellow with black stripe wire): Main motherboard cable and video card auxiliary power connector.

A Radeon HD 6870 that adheres to the reference design can draw up to 14 Amps if you were to run Furmark or OCCT GPU stress testing.

A more realistic draw would be 10.7 Amps.

If you were to use a 4-pin Molex peripheral to 6-pin PCIe adapter cable you would be drawing power from both +12V rails so in theory it should be able to handle it.

i thought it needed 28 amps on the 12v rails?

I'm talking about just the graphics card itself, not the entire system.

With no overclocking the power supply should still be able to handle the power requirements of the system until you're able to replace it with a higher quality power supply unit.

ok.......in many reviews,i read 28amp thing and thought that the card needed 28 amps   ......anyway the psu can surely handle the card for atleast 4-5 mnths?

It will be fine if you keep the total system power draw under 320 Watts.

that is not under my control......
i read on guru 3d that a system with the following rig
Core i7 965 / X58
HD 6870
8 gb ram (probably)
1 or 2 TB HDD
consumed 295 watts in total....
Here http://www.guru3d.com/article/radeon-hd-6850-6870-revie...

I wouldn't risk it. If your PSU goes down it could take the entire system with it. That's unlikely, but why not get yourself another $80 500+W PSU instead and just be done with it??

if i could i would've already bought it.....but i bought this PSU recently so no chance of getting a new PSU  

Well then, your other safe option is to return the HD6870 and get nothing more demanding than a HD6850, perhaps a HD6770.

Listen to K0888...you can use your current PSU as a temporary solution. If you recently bought the PSU, then is it possible to return/swap it with the vendor for another PSU?

DO NOT use cooler master elite . They are not good products. I suggest get good corsair or seasonic unit around 5K.