Everything seems to work but nothing on the screen at all.

Hello, It sounds like when you were taking it apart you disconnect the display screen cable or some other wire connectors, Check them all.

few things to try.
remove battery and just boot off power cable.
remove hdd and see if you can get bios screen
reseat memory
if you have 2 memory chips try removing 1 first, same proble the replace and then do the other

try an external monitor or tv

most laptops require this to be enabled by pressing a function key and an F key.

this should either fix or narrow down the faulty part

What I recommend is you remove everything you could possibly remove from the laptop (HDD, mems, cd rom, wifi cards, etc) just to check if it will turn off even when it's not booting or posting. Try turning it on with just the charger and WITHOUT the battery and see if it stays on. If it doesn't, then most likely the mobo itself is the problem.

u have to press and hold the power button for fifteen seconds to shut off, and it seems to me that your video card may be loose or bad or your memory may be loose or bad.

what u may have done is wwhen u were installing the new board, gave a static shock to the system...that will cause only the fans to come on and nothing more...this is a bad problem bc u cannot fix it...if u figure out something else is wrong, and it gets fixed, let me know

If the system appears to power on, but you do not see anything on the screen, there are several methods to determine the problem at hand.

Make sure the cooling system is fucntional.. a bad CPU fan has been known to make the computer power on, but halt and do nothing to protect the CPU. Some CPU fan's have speed sensors, and other do not, some motherboards require the speed sensor to be functional, or resistance in the line.

Some mainboards will function enough to power the system up, but go no further due to onboad componant failures such as bad / broken SMR, SMC, or capacitor. If you are sure the mainboard works, and the monitor is known to function, proceed with the following troubleshooting tips.

1) Remove everything but the memory, GPU, CPU, and HDD, see if boot is successful, if not Step 2)

2) Replace the Power supply, under powered PSU's can make a system unresponsive / fail to make it to POST, if fails step 3)

3) Replace Memory, if fails, 4)

4) Replace GPU.. if fails, 5)

5) Replace CPU, a non-funtional CPU will alow everything to power up, but will not allow POST in some machines.

6) Replace Motherboard, if fails, start at step 1)

The battery indicator on the handset tends to be misleading. You may need to replace the battery, or if the phone is under a year old, try charging over night. Simply unplug from the phone jack, leaving base plugged into power.

Make sure the BIOS settings are correct for the microproc and also make sure the motherboard supports a dual core processor.

2003 relic day
dvd try dead sure. means power is dead.
ever work before? now? not told at all, 1./2 of all APG cards do not work here, so history of all that matter huge for old legacy pain boxes. I call them.
this pig has SIS chips and we never use those now why mess with any SIS stuff, (eol and doa) both now and ouch 2, ITE 8705 chip !!!!!

Replaced power box fans not oscillating (surge?) anymore hdd LED stays on permanent .
video card LED stays on permanent
.2 fans of 3 going on video card (will gpu controls that not you)
agp 8x fan works(spins)
no power 2 dvd player.
hdd drives dont appear 2 engage but lite shows on permanent .portable hdd lite shows permanent green when plugged in seems something on motherboard blown should be fixable dont know what or where,
well we do tests, not guess or go broke fast.
so the PC is dead, VGA port dead, monitor is good this old most are not good CCFL lamps dead, in MON, no monitor told at all
nor how connected sure AGP

the PC any PC is tested first stripped down so do that first.
no express PCI , no sata drives allowed
no VGA jack on mobo,
best test is old legacy PCI only VGA card to get bios working
AGP only works if on the gigabyte QVL list. not told yours.

wrong AGP card will blow up the mobo, so doing that is DOOMED
the manual tells this on page 1 it is so important it is there.
x4 or what
1.8v agp is blow up time.

1 x AGP slot (8x/4x, AGP 3.0 compliant), supports 1.5v display card only<< read 3 times for effect, then use only allowed cards here.
or use cheap old PCI VGA card, in PCI slot. there is no express slots..
some mobo do not have automatic VGA chip feature.
and is huge huge pain that then. some default to AGP
and if true here ouch./
the coin cell did last 14 years 17-3=14. sorry not possible. replace it.
XP max support, 2001 OS ,21 years old now.

ok your manual said


Gigabyte motherboards will auto-detect the external VGA card after it is plugged in, so you
don't need to change any setting manually to disable the onboard VGA (great this is so PCI cards come up even after new coin cell()

check the transformer...it carries power to everything