Hallo all.  I've asked plenty and it seems like nobody has answers, hopefully you can help. I've built my pc in December and had no problems until Sunday.
 
Intel G33 LGA775 FSB1333
Asus Nvidia Geforce 8800GTS, 640mb
Intel Core 2 Quad Q6600
Kingmax DDR2 1gb x 4
Hitachi 500gb
 
I was playing a game and all of a sudden the picture was lost, absolutely nothing on the tv screen.
Then trying to switch the computer off and on - got 3 long beeps every time.
Took out video card - and used the integrated one - no picture.
Plugged a normal monitor into integrated card - picture did appear but it only goes up to the startup screen and then it just goes to the screen where it asks: Save mode, Start normal, Last known good ... etc.  
Doesnt matter which one I choose - it just starts the circle again.  There are no beeps at startup now. I did change the Ram, problem stayed. Played around with everything and got an error saying that cable disconnected / media not found.  
 
I've taken the hdd out of my computer and connected it with a borrowed pc.  The borrowed pc did pick up my hdd and I could browse files.  I then took out the borrowed pc's hdd and tried to start up the pc with only my hdd.  Once again the circle of reboots, without the pc actually shutting down.  
 
I then tried a borrowed hdd in my computer (leaving my hdd out) - the same thing happened, circle of reboots.  
 
I dont know what to do now...  
 
 
 
 

What's your psu?

It's 400w.  You think that is the problem?  And why is my hdd also crashing in another pc?

The pc doesnt power down and up, it simply goes up to the lock-on screen and then immediately to the F8 screen.

You can't exchange hard disks from different computers if they have different chipsets. You need to do a Windows repair on the other computer to get back to where you were.

When I ran the Xp cd (prof) before swapping hdd's I got the blue screen of death every time before I could get to the repair screen. ... Luckily the borrowed computer was ok after I've put it back together.

I didnt mention that before my pc crashed completely, I had a problem of receiving the blue screen after starting up the pc every 1 out of 10 times.  I thought that maybe I had the wrong drivers for my Nvidia installed.? Can that be the problem for complete failure?  

Are you overclocking?

If you have a spare power supply, try that.
Tell us the brand of your power supply and look at the label and tell us how many amps are on the 12v rails. I'm pretty sure your power supply is not adequate for your system.

Its a NZXT PF400
DC output +3.3V  + 5V    + 12V   -5V    -12v      + 5VSB
MAX A.       22A      35A       20A    0.5A   0.8A      3A.
 
Thanks for helping.

No I wasnt over clocking, but my daughters 'clever' boyfriend was playing games while I was  outside - he could have changes some settings in Asus.

What error message did you get on the BSOD?  Also, try pressing F8 when booting off the hard drive and select "Disable automatic restart on system failure" and see if it's giving you a BSOD before rebooting.  Might help narrow down the problem.
 
And which Intel G33 board is it?  I see three listed on Intel's site.

I disabled automatic restart and immediately got BSOD.  Information on the screen:
A problem has been detected and windows has been shut down to prevent damage to your computer.
If this is the first time ……
Check for viruses on your computer.  Remove any newly installed hard drives or hard drive controllers.  Check your hard drive to make sure it is properly configured and terminated.  Run CHKDSK / F to check for hard drive corruption, and then restart your computer.
 
***STOP: 0X0000007B (0XBACC3524,0XC0000034,0X00000000,0X00000000)
 
The mobo is D81072-306  

I get exactly the same message when I run the xp cd - even before I can get to repair.

Two things:
First, the 12 volt out of your PSU is inadequate - especially with your video card.
 
I have a Q6600/GA-EP35-DS3P/eVGA (G80) 640 MB 8800GTS system with 320 GB HD and LG DVD drives breadboarded on my work table. Using a calibrated clamp-on AC-DC ammeter (AEMC MD400) to measure current, I get:
 
12 volt CPU connector with Q6600 running Prime95 - about 8 amps.
       OC'd to 3.3 GHz, vcore from 1.2625 v to 1.3125 v - about 9 amps.
12 volt line to motherboard in main PSU plug - 1.5 to 2 amps.
12 volt graphics card connector while running 3DMark05 - 7 amps.
The two drives - 2.5 amps.
 
That's nearly 21 amps under load. And that doesn't include the other two 500 GB drives or all the fans in the Antec case that the system will go into.
 
Second, a series of three long beeps indicates a memory problem.
Suggestion: Remove the video card until you get a better PSU and use the onboard graphics. Check the manufacturer's specifications on memory operating voltage. Pull all four sticks of memory. Boot. You will hear the 3 long beeps. Test each stick individually. If they each work, go into the BIOS and adjust the RAM voltage to specs if necessary. Then test them in pairs.
 
Last, once your system is up and running, password the BIOS to keep other people out of it.

Thanks, the video card was the first thing that I removed and still had the same problem.  I will try the ram now.

With only 1 stick I get the following message:
PXE-E61: Media test failure, check cables
PXE-M0F: Exiting Intel Boot Agent
No bootable device --- insert boot disk and press any key
???

I tried the xp cd at this time and still got the BSOD.:cry:

I disabled all boot sequences but cd and hdd and tried running the xp cd again. This time I got the following message:  
File usbohci.sys caused an unexpected error (1024) at line 5897 in d:\xpsp1\base\boot\setup\setup.c
Press any key to continue.
 
.... Computer restarted and did the same @@@ again.

8800GTS 640 requires:
 

7B stop code details:
 
http://support.microsoft.com/kb/324103
 
Try clearing cmos, either replace the gpu with a lesser one or get a better psu, try each stick of ram in each of the slot until the pc posts, then set up bios, install the rest of hardware.

I'v got no idea of how to clear the cmos?