POST issue

Hi All,

I am facing with a weird issue. I tried to do all that I can but I am still not able to figure out the problem my computer is facing.
My system is more than 7yrs old and i feel its time is almost up. I have the specs with me

Processor: Intel P4 2.66 Ghz
Motherboard: Intel D915GAV
Ram: 1GB Transcend (1.5yrs) and 512MB Transcend (7yrs)  
Hard Disc: 2*500GB WD SATA
Graphics Card: 8800GT
SMPS: Corsair 750W

Issue

While copying a lot of files to my external Hard Drive, watching movie, surfing on net and downloading suddenly my system just turns off. On trying to start is again I hear a single never-ending beep. Turned off the computer again and turned it back on the beep was gone but on POST as I wasn't even able to see the Manufacturer Screen.


Steps taken to resolve the issue

Few days back I faced a similar issue and I just took out the CMOS and inserted it back again and my computer started running. I tried that step but no luck. Had also bought a new CMOS as i suspected that the present one was done for but still no luck
removed the RAM, re-inserted it back again and still no luck.
Added Thermal Paste as the system might had shut down due to excessive heat still no luck.

Finally I tried starting the system only with a single stick of RAM 1GB (without the Graphics Card) and viola, Finally I was able to see my desktop after few hours of labor.

I turned it off re-inserted the graphics card and turned it back on and there was that single never-ending beep. So presently my system is running properly but without the graphics card.


Possible Causes

As per what I came across the following below are my possible conclusions:
1. RAM has become weak
2. Graphics Card slot or the Graphics Card is not working
3. motherboard has become weak


Please share in your views. Though my system has taken a lot of pounding i still believe there some life still left in it. Its Not just me, my system too would appreciate your help.