Hello, i am using RADEON HD7850 on mine PC, and i pluged into it 2 monitors:

1. LG Flatron w2452t by a DVI port 

2. Packard bell Maestro 223DXL by a VGA port (dvi-vga kable)

And i got a massive lag, when playing 2 wideos (not even HD) the whole pc gets glithy and laggy... Screens work in 1+2 mode, the LG is primary and Maestro is seckond. When im using only 1 monitor everthyn is fine and super speed, but in 2 monitors mode i even cat rlly play in low tech games. Drivers are latest from the site for Windows 7 x64 wich im working on. In the device managment the monitors are seen as PnP monitor (what ever that means).

I used the same monitor on mine old PC where i was having GTX 260 and it worked fine and smooth.

Will be gratefull for any solution

This is mine PC

Procesor: PROCESOR CORE I5 3330 3.0GHZ LGA1155 BOX (BX80637I53330 921407) 
Mainboard: MSI B75MA-E33 INTEL B75 LGA 1155 (PCX/VGA/DZW/GLAN/SATA3/USB3/DDR3) MATX
RAM: GOODRAM DDR3 8192MB PC1333 CL9 (GR1333D364L98G) 
G-card: ASUS AMD RADEON HD7850 1024MB DDR5/256BIT DVI/HDMI/DP PCI-E (860/4800) (HD7850-DC-1GD5) 

Make sure you have enough GDDR memory to support the extra textures the GPU has to handle with 2 monitors. Usually 1GB isn't enough for 1 monitor. Or you can buy the same gpu and crossfire them for better performance and multiple monitor support

Bah, 1gb is more than enough for multi monitor setup, hell i was playing dvd's on a tv connected via vga cable on a 64 meg gpu like 7-8 years ago. Now a few practical questions, what are your core and memory clocks when playing videos on multi monitor setup (easiest way to see them is with gpu-z) and what player are you using to play them? Are they running in windowed (or full screen borderless windowed) or full screen D3D mode? Do they use DXVA?

Yea, i was running 2 monitors in lot less GDDR and there was no problems.

BUT i checked things today, and i unpluged the seckond monitor (maestro) so the one left is Flatron connected by DVI (the bottom plug on the card, not the one by HDMI's). And i still got lags ! The problem is with a game "world of warcraft" when it runs it glithes whole mine PC, im running sometimes 1 and sometimes 10 windows with that game, and there were never problems, only now, after using the PC for like 2-3 weeks. 

So i think its the game (as i always got it running in the backround) lags the PC, but this problem is fresh and i was running the game before with no problem on the same PC/Windows/Gfx drivers. So i think i installed smthn mainwhile that sloows down the game, im posting mine settings on the PC, so plz check them if everting is OK, if yes, i will look for the problem elswere.

So check plz this screen shot with the settings, is everything ok?

http://dl.dropbox.com/u/4823825/PC%20settings/Bez%C2%A0tytu%C5%82u.jpg

You were playing DVDS, that require absolutely no gpu power at all. It's a game for god's sake

Why do you have your power control set at 0%? Try it at +20.

Intel I7 960 @ 3.87ghz *Intel DX58SO *HIS HD6970 2gb *Corsair TX650M *2x4gb Corsair XMS3 *WD Black 1TB *Windows 7 Home Premium 64bit *Gateway HD2401 24" 2ms 1920x1200  ***Asus N71Jq laptop *Intel I7 720QM Processor *Mobility Radeon HD5730 1gb *8gb Ram *Windows 7 64bit  ***Acer 5750 laptop

* A clear conscience is usually a sign of bad memory *

Well im not the most advance person on the whole GPU thing. 

Any hints what i could change in the settings to run as much as possible game windows in lowest quality and resolution possible. So i can run a max number of them, not laging the PC? 

I just gave you one....move the slider all the way to the right. +20. Are you trying to save electricity? Move the slider....don't forget to hit "apply".

Intel I7 960 @ 3.87ghz *Intel DX58SO *HIS HD6970 2gb *Corsair TX650M *2x4gb Corsair XMS3 *WD Black 1TB *Windows 7 Home Premium 64bit *Gateway HD2401 24" 2ms 1920x1200  ***Asus N71Jq laptop *Intel I7 720QM Processor *Mobility Radeon HD5730 1gb *8gb Ram *Windows 7 64bit  ***Acer 5750 laptop

* A clear conscience is usually a sign of bad memory *

oh yeah they do require gpu power, i was making an example with a very old pc! with modern hardware obviously it seemingly consumes nothing.

Yea, i just fixed it, electicity is not the problem at all, anythyn more ?

Try a DirectX 11 game, not 9