Old Hp slimline 400-34 not showing display

[Donutmuncher]

Hello everyone. I have this old computer that I have not used for maybe about a year and a half. I decided to try and fix it since I could put it to use or give it to someone. The specs of the hp slimline can be found on this link here http://support.hp.com/us-en/document/c03791266. My problem is that no display shows at all, but the computer turns on. Currently it's Windows 10, but it was windows 8 before the upgrade. Patio said that if I can perform a factory reset, it will work again because it won't have windows 10 anymore. I looked up methods and tried one where I press f11 and move to the reset option. The computer only has dvi connection and thats how I connected it to the monitor. I know the monitor works since I tested it on another computer. Any ideas?

[Geek-9pm]

Can you see the BIOS splash screen?
Can you get into the BIOS setup?
You said windows  was working on it?  When?

[Donutmuncher]

Nothing shows up on the screen, so I'm not sure if Bios can actually pop up. I'm not entirely sure when the last time it worked, but it was about a year ago.

[Geek-9pm]

hat about keyboard lights?
If you can turn on or off the caps lock light, then something is working. The CPU has to be running to do that.

What about fans?
Can you hear the HDD whine?
Smoke?

[Donutmuncher]

Keyboard: The lights turn on for a second and then nothing works, cap locks light does not work

Fan: I do hear fans

HDD: i dont hear anything besides the fan

I do not see smoke

[Geek-9pm]

OK. With no caps lock, the CPU is not running like it should.
Some possibilities:
 ▐ CPU jumped out of socket. Earthquake?
 ▐ Graphics card dislodged. Ignore this if it has only integrated graphics.
 ▐ Memory stick dislodged. Or gone bad.
 ▐ Power supply shut down.
 ▐ HDD has frozen and forced system to stall.

You can disconnect HDD and also CD-ROM drives. This will reduce load and power supply and should force the BIOS to display some kind of message.

Also try one stick of RAM. The the other.

[Allan]

If nothing shows up on the screen:

1) check all connections to the display

2) try a different display

[Donutmuncher]

I'll have to test everything out when I get home, but thank you for all the replies. I will let you guys know when I have tested out everyone's tips.

[patio]

If it's been sitting that long you may wanna also replace the CMOS battery...Part # CR2032...
Also remove and re-seat the RAM stiks...

[Donutmuncher]

Alright, I'll be sure to check the Cmos battery as well.

[Donutmuncher]

I reseated the ram sticks and tried a different display, but it didnt work.

things that i havent done yet: cmos battery suggestion and removal of HDD and CD ROMs.

The cables are really tight and I have remove a lot of things to get to hard drive, but I will do it. I will keep you guys updated

[Donutmuncher]

I tried out another PSU and replaced the cmos battery which seems to have solved the problem. I will try to factory reset it now and revert it back to its original windows. Thanks for all the support!