Will not power up

first thing first check power plug make sure it is plug in and its not lose or some cat/dog or something didn't get a hold of it also if your running a power strip check make sure its working and it didn't trip the fuse. two on the back of the computer where the power supply is there is sometimes a switch try flipping and seeing if it will start. if none of this is your issue then it is time for a new power supply which unless this is a gaming pc you can get for about 50 or 60 from your local pc store.

Check cable first rats might be the culprit then replace power supply.

You can download the service manual from this WEB site.
ftp://ftp.dell.com/Manuals/all-products/esuprt_desktop/esuprt_xps_desktop/dimension-g4_Service%20Manual_en-us.pdf

The CMOS battery is a coin size 3 volt lithium battery type CR2032.
Replace this flat battery then go into the BIOS setting and set the Date & time save and exit.
This should fix your problem.

Check CMOS and Memory Modules:::If the error message is "UNEXPECTED_KERNEL_MODE_TRAP," then it indicates you have problem with the memory of your computer. You need to check whether the SIMMs (Single Inline Memory Modules) are compatible and have the same speed. Secondly, also check whether you have set the CMOS (Complementary Metal Oxide Semiconductor) to the right amount of RAM. If these solutions do not work, you might have to replace memory in your computer....try to use system utility tool like Reginout.. Hope the problem is resolved.

You will have to go to the Dell website and create an account. Here you can download manuals for you product line. I've replaced motherboards on that model before, not easy.
http://www.dell.com/support/home/us/en/19/product-support/product/dimension-g4/manuals

I believe you have used the wrong type of CMOS battery. Try putting the old one back in and see if it will boot. If not the CMOS NAND chip may be broken. If this is the case contact Dell and order a new one.

Both the system password and the BIOS password are set in the BIOS CMOS. You need to clear the CMOS.

The online Dell service manual for the XPS 400 provides a clear and detailed procedure for clearing the CMOS. It's just a matter of moving some jumpers around:

http://support.dell.com/support/edocs/systems/xps400/sm/index.htm

If you are not used to working inside computers, start with "Removing the computer cover", then go to "System Setup" and click on "Clearing Forgotten Passwords".

Another method is to unplug the power cord and remove the CMOS battery for a 1/2 hour or so. For details on how to do that, try this website:
http://www.askvg.com/how-to-reset-remove-bypass-a-bios-or-cmos-password/

i gotta know 1st what is ur system configuration..is all ur system is getting power on..is there any sound coming out of the system..
assuming that the bios has not been flashed in a wrong way & u r a professional..

before u proceed to complex checkups..check the mains power supply- the fuse/switch/wirings/power cords/other associate circuits..

probably itz either minor case of loose ram/improper ground/cmos battery..
or major case of faulty or defective smps/cpu/main board short/display adapter or card/monitor

..plz do check the following as in order:..

1) in power on mode, open/unplug the data/vga cable of the monitor from cabinet..see if raster or 'osd' is appearing on the monitor screen..if so monitor is ok..else replace the monitor and see..

2) if u hv a graphics card, replace with a standby or onboard and see..

3) see if the ram(s) is loose/faulty..open clean/remove carbon & or oxide formed on the teeth with an eraser n resit it..or replace with a standby n see..

4) unplug mains supply..pick open/remove the cmos battery..check (above +3v)..resit..

5) remove/clean dust neatly..dust is non-uniform in nature n may cause jam/short circuitry/excess resistace n many more..resulting an increase in heat..

6) open the CPU Heat-Sink with fan out of the socket..put some "Heat Sink Compound" (available in local electronics chip level spare market) between the cpu/processor and the CPU Heat Sink *** fan..resit/fit it tightly in position..

7) the smps itself may b defective/faulty..check the outputs of smps viz. 0v (black~ground); +12v (yellow); +5v (red, green~ps-on, violet~pg & grey~sb); -12v (blue); -5v(white); +3.3v(orange)..
the 'oscillator and error amplifier ic', or pwm switching regulator circuit..look for defective protector-transformer/resistance(esp 4.7k)/mosfet..

8) if itz not the smps, then it must b ur main/mother board..see with a debug card for mb error..may b short..look for defective capacitors(esp above 1000mfd)/mosfets..go through the mb's south bridge n the circuit lie around atx connector..the crystal clock generator (if cpu isn't heating up)....

always better to seek advise from ur system admin/vendor....

flaky power supply

No they change out the whole motherboard and in saying the its invasive and costly and there is no way you can buy a video card for a laptop there all on the motherboard.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/edwy_1a56970cf1ea4620