I just got my hands on an 8800 gtx by MSI (used - Guy says it worked fine for him).  Unfortunately it is only about half as fast as my 8600 GT OC by MSI.  3dMark06 - 3078 as opposed to 6034.  Some said it was my Power Supply, which was an OCZ 700 Watt Game X Stream.  While I doubted this, I bit the bullet and put in an 850 Watt Silverstone with 70A on a single rail.  Nothing.  Still extremely slow.  Uninstalled drivers, reinstalled latest drivers, tried Driver Cleaner Pro, nothing.
 
Temps idle on GPU at 44C with fan at 75%.  GPU-Z identifies all aspects of card fine and it is running at its default speed of 610Mhz/2000Mhz.
 
I am at a loss as to where to go.  Anyone have an idea of what to try?
 
Comp Specs:
 
DFI Lan Party NF590-SLI M2R/G
AMD 5000+ BE 2.6 @ 3.2Ghz (Water Cooled)
2 GB OCZ PC6400 4-4-4-12
2 74Gb WD Raptors in Raid 0
1 DVD Writer
Winblows Vista 32 bit
 
Thanks.

Did you install updated drivers? Did you forget to plug in the pcie power?

Yep, tried the 169.25, 169.44, and the beta drivers 174.74? i think that's the version.  Also, both PCIE 6 pin connectors are plugged in.  I haven't recieved any messages about the card being underpowered.  Which reminds me... where in the world is the Nvidia Power Sentinel everyone is talking about lately?  Automatically installed?  Hiding somewhere?  Needs to be installed seperately?
 
Thanks again.

 
 What are you playing and at what res. Also what do you mean by slow as in what FPS are you getting ?

Best bet is some thing is wrong the the graphic drivers. Also some thing could be running in the background. Also are both cards installed (8600 and the 8800) or just the 8800?

It's weird that it is so slow... But since you swept with driver cleaner and reinstalled drivers I don't know if there is anything more you can do except reinstalling motherboard drivers ( download latest ) or finally reinstalling Windows. If the card itself is 100% working that is.

Just the 8800 gtx is installed.  I've run Windows Vista Experience index and it is rated at 5.6 for this card.  So was my 8600 gt.  
 
3dMark06 is getting 7 - 17 FPS with all the benchmarks.  Haven't tried any games.  Figured it would be pointless at the moment.
 
I suspect driver problems too.  Even after running driver cleaner, I had a time when the card wasn't recognized by windows as an 8800gtx, but would only detect as a Standard VGA Adapter.  It took about 3 uninstall/reinstalls of the drivers to get it to be recognized properly.
 
As much as I hate to do it... I may have to end up formatting and reinstalling...
 

Oh yeah, I tried updating the Motherboard Nforce drivers last night too.  Still no go.  :-(

One question for you 8800 Card owners... Is your "Change Settings" button available for changing hardware acceleration?  Because mine isn't.  It is greyed out and unclickable.  So I can't change video hardware acceleration.
 
Thanks.

had problem like that with an asus 8800gs only got about 4150 with 3dmark06(defalt settings) on a gigabyte 965 motherboard with 3ghz core 2 duo    same card scores 9100+ on my slower 5000+am2   found out card was  only running at pcie-x1 when benchmarking but pcie-x16when just running desktop found this out by downloading and running gpu-z..........
  fixed the problem by raising the voltage to the pci express graphics in the bios    your dfi motherboard will have something like that  my 8800gs now scores 9800+ stock 11200+  oc  hope this helps

Hmmm, GPU-Z says that it is running at 16x in the PCI-E slot.  I'll have to check and see what the bios says, and check the voltage.
 
Anyone have an answer on the Hardware acceleration question above?  That one is driving me crazy.
 
Thanks everyone for your help.

Nice one Daautin. I've been having the same problem on ,mine. I Kinda came tot he conclusion that my mobo is dying or something. I was guessing that the lanes were shut off too, but it says that they are running at 16x. How do you check it when running a game or something? How much juice did you give the pcix bus?

Well, nevermind. I would like to think that an Asus Crosshair would have some tweek options in the bios, but no... No Options for voltage or changing the pcix lanes. GPU=z says it's running at 16x. But dont know how to check if it's for sure staying there when under load.

Well well well. I don't know how, but it seems that although everything was set right in the bios, Ntune had set the HT multiplier to 1x. Now my performance is much better @ ht 1075mhz than at 215mhz!

Wow.  Wish my problem was that simple.  But GPU-Z says I'm running a full x16 PCI Lanes and the Core Clock and Memory Clock are running at full speed too... sigh.  I'll probably try a format, just as soon as I find out whether or not missing the Hardware acceleration option is normal in Vista or not.

Well, just ran Far Cry and in the Auto Detect Video options it says that my machine specs are HIGH, whereas my 8600Gt was ranked low.  So it sees the card for what it is, but I am getting artifacting during gameplay.  I'm just gonna format and try that yet.  
 
Thanks for the help all.

to inglburt or anyone else i raised the voltage up just 0.1 volts to the pci express overvoltage control in the bios may be called some thing different with other makes/types of bios