Hi,
yesterday I bought GA-EP45-DS4 card and installed a system based on Intel q9450 processor with it. However the system doesn't seem to work properly. After powering up one short beep produced indicating that all ok, than I'm unable to enter the bios cause neither of my two keybords seem to work using usb port, after that system goes to a constant reboot cycle.
Two times I was able to use keyboard to enter the bios which seems strange to me but after entering it the system stuck and doesn't response to keyboard commands again.
I've done the clear cmos and this doesn't help. I disconnected all the expansion cards and hdd's the same. I think it should be a power issue as 450 w couldn't be enough for such a system with quadcore cpu and I uses ATX 2x2 12V connector to supply power to it.

what your opinion on this situation and what could you suggest to me?

P.S. The next strange thing I noticed is that cpu load mb indicator shows the full load at the post. Is it normal?

I suggest that you try using a PS/2 keyboard for working with the BIOS.

thanks for fast reply, I already found this workaround and will try it when I'll be at home.

anyway I'm planning to buy new psu for more watts headroom.

It looks like the PSU is the problem.

I had the same problem with a Corsair 750TX PSU, the powersupply was defective and gave me rebooting problems. It rebooted several minutes into my first system boot up. After I keep booting the system, the time between reboots was shorter until it didn't boot ever again. After putting my 430W Antec NeoHE in, the system booted and has been running flawlessly now. I bought the 750TX because I didn't think my 430W NeoHE could handle the system, turns out it can.

Constant reboots are usually the PSU fault, not motherboard or CPU. I'd recommend a Corsair 750TX PSU, even though the one I bought was defective, it's a very nice PSU for the money and is very quiet. I just got bad luck and received a bad one. I returned it to Fry's.

oh yes sorry, this is the full setup:

GA-EP45-DS4 rev. 1.0
Intel Q9450
XFX 6600GT
Corsair Twin2X2048-5400C4 (2GB); TWIN2X1024-5400C4PRO (1GB)
Power: Chieftec GPS-450AA-101 A (450w)
DVD-R/RW Plextor PX-760A
Maxtor 7L300S0 300GB, Seagate 7200.9 160GB, 7200.10 500GB

pcgamer12, yes it seems to be.
also I've made a little mod to my chieftec PSU before installing it: replaced 120mm fan powered from 2pin slot on PSU chip for more silent one with 3pin control to use mb pwr connector. Have no clue if it could be an issue but fan works much slower now so my guess that psu could be overheated.

450wattsw is way more power than you need for that system.

I don't know much about Chieftec PSUs w/o looking, so it may be a bad PSU or your mods may have effected more than you expected.

I guess my mod is nothing special really but maybe removing the 2pin connector from psu chip resulted it thinks that there is no fan at all. but it really weird cause I reinstalled vga cooler same way and it works with zalman fan control.

also early resetting issue could be a result of the issue discussed on silentpcreview forum:

"In a minimalist system where on-board graphics is used, this 12V turn on delay in some motherboards causes the initial total current on the 12V line to drop below 1A. If the delay is long enough, then the PSU will not start."

I noticed that cpu cooler starts to work only within few seconds after powering my system on so it could be some how related to aforementioned problem

In your system, do you really have a 6600GT or an 9600GT?
The reason is the 9600GT uses quite a bit more power than the 6600GT.

The 6600GT could almost be considered minimalist, while the 9600GT definitely is not.

yes I have 6600GT and I don't really need more as I don't play games or work's with graphics. I just updated my old machine with new mobo and cpu thats it.

A similar problem occured on my DQ6 version of the board. I cleared the problem by turning off the power supply, removing the battery, and clearing CMOS. This effectively reverts the bios to factory settings. The first boot the board did it's "Configuring Storage Policy" thing and auto-rebooted. The second boot automatically went into bios as if this was the first time ever being powered. I loaded optimised defaults and restarted. The third boot it was ready to be configured as I wanted.

I don't agree with this at all. I have had constant reboots due to overly ambitions overclocking settings - such as setting my RAM timings too tight or my FSB too tight. I don't think the PSU is the first thing to blame in this case, though I wouldn't rule it out - I'm just saying that many things can produce similar behavior.

As for a CMOS reset, you often don't have to actually remove the CMOS battery even, but can simply flash the BIOS by shorting some pins. I know my Gigabyte board has a pin that I can short to flash the BIOS back to factory settings. I had to initially do this to get my board to boot.