'Tatty One' does make a good point in his post above in that flashing a non reference card can be potentially lethal.
It's a shame you didn't inform us of your System Specs as this would have been enormously helpful to those of us Geeky enough us to potentially help you out.
Anyways.
I feel the most logical thing for you to do is download and flash your card with its original\default BIOS just incase the current BIOS is the culprit (whether caused by over fiddling or just bad luck it matters not).
Give that a try because from my experience using a newer BIOS from the same or different manufacturer is more than likely going to achieve no gains whatsoever over your cards original\default BIOS and you also have the possibilty of bricking your card as a real and present danger.
I always find the best and simplest way to fix any PC problem is by returning to the 'Default Settings' as supplied by the manufacturer (in this instance by BIOS flashing).
You must also keep in mind that it may not even be the card at fault and that you have infact a compatibility\gremlin or other problem lurking about.
I gather this card is a recent purchase so i wonder if you followed the golden rule when purchasing new components and asked yourself, 'How will this new hardware interact with all the other components in the System'.
The only way to find that out pre purchase is to research, research and more research.
I offer you all my System Specs as an example of a quality, well rounded, well thought out Gaming Rig that has never run out of headroom and won't need updating anytime soon.
Motherboard -------Gigabyte P55-UD5
CPU----------------Intel i7 860 (oc'd to 3.2)
CPU Fan------------Zalman CNPS9900A LED
RAM----------------4Gb Corsair Dominator GT CMG4GX3M2A1600C7 1600mhz (7-7-7-20)
Video Card----------PowerColor Reference 5870 (oc'd to 875\1250)
Hard Drives---------1x OCZ RevoDrive PCI-Express SSD 50GB (recent addition)
--------------------4x Seagate 500Gb ST3500418AS (RAID 0 Twin Drives Multi Partition Config)
PSU----------------CoolerMaster R5-550-PCAR-E3
Mouse--------------Razer Mamba
Keyboard-----------Microsoft Cheapo
Case---------------CoolerMaster Elite 335
Monitor------------ Samsung 27" P2770HD (recent addition)
OS-----------------Windows 7 Ultimate
This System has never Crashed, CPU has never gone over 45c, 5870 has never gone over 65c, it idles on 630mb of RAM, RAM temps are so low as to be insignificant, and to top it all off i can play any current game (Crysis included) on High Settings without stuttering, (mainly BC2 though, 115+ fps, all high settings, 1920x1080 res, no AA or AF, no Bloom, Catalyst on High Quality MipMaps).
Keep in mind that i am also an Advanced System\Registry Modifier as i prefer my PC's not to go off into their own little realm of menial tasks and to concerntrate on what i'm doing, lol.
Well I'll end this little speech with a Thank You to those that bothered to read it.