For unknown  cause the POWER SUPPLY had short or something and u can smell smoke .
When i opened it u can see the burn  ,its model ATX-300GU  which has P4ATX 12VX1 connector .
I have an old power supply from an old PC but it doesn't have  the P4ATX 12VX1 connector .

would that make any different if i replace it , because when i did the power runs but all lights are steady and the monitor is not turn on !
Could that connector be the issue or it's not important connector ?
Second , could that short have burn the HDD too? " the PC was off when the smoke and the smell from the power supply happend ".
i just don't want to buy new one if the one that i have could work .

Thanks.

I hate to tell you this, but you need hands on trouble shooting at this point.  If your PSU went out so badly that things were smoking it could've damaged the motherboard or some daughtercards.Could that happen to the MOBO even if the PC wasn't running?

Pentium 4 require the extra connector  for the processor....if you SMELLED burnt ELECTRONICS, good chance it's the PSU....where do you see the burn marks...on the supply or the MB?....to be certain swap in a known good power supply, thats the cheapest way to go, considering the burnt odor.

" If your PC is a newer Pentium 4 or Athlon 64 system, you'll have more than one connector running from the power supply to the motherboard. Both of the newer CPUs usually require an additional 12V header, a 4 PIN connector arranged as a square 2x2. High end motherboards like the ASUS with PCI Express can also use the 4x1 drive connectors to supply additional power to video cards by way of the motherboard."


http://www.fonerbooks.com/r_power.htmIf your power supply is smoking, time for a new one