My husband and I vacuumed out the INSIDE of our tower as we have done QUITE a few times in the past. We hooked everything back up to it when the hard drive refuses to boot up. The monitor screen is black so I am assuming it is in the system? ANYONE able to help out. I would hate to replace the machine. It is several years old but still a goodie. It is a 40 GIG Seagate Harddrive with running 512 sdram. To replace this computer is more than I have got right now. Please I am so desprate, help me figure this booger out. So I can get off my laptop.
Thank you very much for your time.
ShellRemove all power sources to the machine.
Ground yourself by touching the case a few times.
Carefully remove and re-seat the following :

Any sticks of RAM..

The video card...

And any other add on cards such as a NIC or other...

Replace all cables and make sure they are firmly seated especially the hard drive ones.

Re-connect the power, cross both you and your husband's fingers and boot up.

Keep in mind that by using a vacuum inside the case that you may have fried one or more of the components as vacuum's produce huge amounts of static electricity which electronic components hate....

Good Luck and let us know. I did all you stated, took me a bit to do it but I managed to get it done. I went to try to reboot the hard drive, I got just one beep and managed to figure out it was the power supply powering up. I can get both D:\ and E:\ to open and close and did show the A:\. I even removed and replaced the cosmo battery. Either the board is just dead or the hard drive is dead. So now how I test for both any ideas?

What I have is a Dell Dimension 4400, 40 gig hd, 512 DDR Sdram,
Well here is the webpage for what this machine contains.
http://support.dell.com/support/edocs/systems/dim4400/specs.htm#1101572
So what is my next step? Cry cause we screwed up and have to put out $200 for a mother board or hard drive?
Thank you again for any help.
Shell Have a look at the drawings on this web page:-
http://support.dell.com/support/edocs/systems/dim4400/techov.htm#1101565

check that the "front panel switch connector " and "front panel audio connector" are connected to the correct locations

does the "stand by power light" actually light up?

check the "processor fan connector" and the small square four pin "12volt connector" is connected to "J4B1"

check that "cd drive SEC IDE" and "hard drive PRI IDE" connector reversed around in each others sockets. and that there are no bent pins in the connectors.

take a break from looking at it, then patiently remove and recheck all connections and each connector.
the obvious often is staring you in the face and is the hardest to notice.
To determine if it is a Hard drive problem hook up that HDD in a known working machine as a slave drive with the working machine's HDD jumpered as Master with slave and see if you can see the drive. If so try copying a few small files to it. If this WORKS it is not the HDD.

p.s This does not neccessarily mean that the motherboard is fried either but it's best to move one step at a time in these circumstances.