Dimension 4700

To get as far as the Windows splash, the ABCD lights would all be green at one point--do they change?  (I'm guessing not.)

 

Windows splash does yield to black screen/flashing cursor during driver loading (next is your wallpaper).  Sounds like that's where it's hanging--suggests a driver is not happy, either because its hardware went bad or the driver itself went bad (both can and do happen).

 

Now, the fan thing.  It never did that before it stopped booting, did it?  Once the system is starting Windows, the fan control has initialized and it should be running moderately under control of the chipset.  However if the chipset stops running, so does fan moderation and fan runs full speed.

 

From these datapoints--assuming they are related--a Windows driver initialization command is giving the chipset an error for which there is no handler (hanging the chipset).  CTRL or F8 and enter safe mode.  From C: prompt\msconfig, disable device drivers (display, sound, net, modem, other) and restart to normal Windows.  If it still won't start, another hardware device with a Windows driver is having a problem--go back and turn off what's left, but leave USB if that's where your keyboard/mouse are.

 

Say it starts OK with drivers disabled (the display won't look right)--turn the drivers back on one at a time until you reach the one that locks it up.  If that hardware is removable/unpluggable, substitute it with a known-good one, turn its driver back on, and if everything works that way, the unplugged device is faulty.  If that associated hardware is not removable (part of motherboard) or a known-good substitute also fails the same way, uninstall and reinstall that driver.  If results remain the same, motherboard appears to have faulty hardware.

 

There are other routes to diagnosing this--above is the most direct one (gives the most answers in the fewest steps)--assuming the fault is more or less 'standard' and it will start in safe mode (it should, but no guarantees).  If it won't start in safe mode, you have to unplug all accessory hardware and see if it starts that way--yes, reinstall one at a time until it locks up--no, you can't disable or reinstall drivers if Windows won't start at all, and the problem is either in unremovable hardware (motherboard) or an inaccessible Windows driver (reinstall Windows).  Blah, blah, blah--I made it sound too complicated--just see if it starts in safe mode and go from there.