I already posted this on yahoo answers but no good answers yet so I'm just going to Copy/Paste the thing:
Computer went in Power Saving Mode and will NOT boot?
CPU: Intel(R) Core(TM)2 Duo CPU E7500 @ 2.93GHz (2 CPUs)
RAM: 2Gb
HDD:320 GB Total
GPU: NVIDIA GeForce GT 240
OS:Win7

computer didnt boot, SO i tried restarting it manually...By then the comptuer stopped booting and the power supply got fried, so I changed the PSU. Now with a new PSU, I still get Power Saving Mode and I cant get the comptuer to boot, I cant even access the bios and the mouse ad the keyboard wont even work.

Additional Details
The power supply cant be the wrong one..
I just plugged the HDD and the main board...I never unplugged anything else in the case, And the problem didnt stop after changing the PSU
try removing the RAMs for a few seconds, put them back in
then remove the bios battery, then put it back in
Zusynoid-x wrotetry removing the RAMs for a few seconds, put them back in
then remove the bios battery, then put it back in
I have a stupid question to ask though:
While the computer turned off ofcourse, I should take out the bios battery, which is the battery that is round shaped only a little bigger than the ones normally found in hand watches ?
yes, of course when it's off
and yess that
HDD is smelling funny.
But then again why cant I even get it to boot.
try checking the power supply, if you can plug in a usb with led light, try to see if led blinks.
haidcar wrotetry checking the power supply, if you can plug in a usb with led light, try to see if led blinks.
The usb blinks and seem to work ok...
Sorry to tell you but it seems that the motherboard is fried too , it happened once with a friend before the same as yours , i hope I'm wrong but it might be it :/
jajoja wroteSorry to tell you but it seems that the motherboard is fried too , it happened once with a friend before the same as yours , i hope I'm wrong but it might be it :/
I had the same problem... electricity in lebanon is.... not so good, which KILLS the motherboard
In other words your motherboard is f***** :S
well I most probably think your mobo is dead. To make sure of that, get a working PSU, 1 RAM module, working compatible CPU, and the main board. before connecting everything, jump start your PSU using a paper clip to see if the PSU fan turns on. if it does, PSU should be fine. hook everything up, not working? mobo problem.

do not hook the graphics card even if you dont have any onboard. the test here is to make sure the mobo boots up normally rather than testing if display works.
As MrClass and "jajoja" said, i think it's your mother board.
When I open the case and start the computer, there's a green LED right on the mobo , It turns on normally...
Does that mean anything ?
ok disconnect the mother board from every thing graphics card, dvd rom, rams... leave it only connected to the power supply. and give it a shot if doesn't work that means its either the motherboard or the cpu.
ac1d wroteWhen I open the case and start the computer, there's a green LED right on the mobo , It turns on normally...
Does that mean anything ?
The lit green LED means that there is 5 volts standby power through the mobo. Not really an indicator that the mobo can boot up. Your mobo might be fried, i would recommend trying out some of the suggestions above.
no it doesnt mean anything except that the mobo is getting electric power. But that still does not mean the mobo is working
Would you try removing the RAMs only and turn the PC on? If you hear beeps it means your motherboard is working. You can also see if the CPU FAN gets working.
do all mobos give error when no ram is installed? i remember a brand called biostar which doesnt indicate an error for missing ram on P31 chipsets