i have a dell desktop.. i restarted my computer the other day and when it would not restart..only stay on the logging off logo..i maually shut it off. now when i try to start it.. it makes a real loud humming noise like a fan..and all i get is a yellow light on the power button and it does not start.. i checked the fan that is in the front.. over the cpu i think.. it is turning but was covered with dust on the solid screen in front of it.. any SUGGESTIONS? it is a dell xps 420. the sound sounds like it is coming from the fwd fan or near it.. thanks!!!You need to do some serious housekeeping inside that case...
A can of compressed air is good for this...along with a soft SMALL paint brush for the stubborn dust bunnies...
Also when BLASTING the fan areas USE a Q_Tio to hold the fan blades in place so they don't get damaged...

As always remember to remove all power sources and take anti-static precautions...

PS: After completing this there MAY be a fan replacement involved...
As long as you take it with you you should be able to find a suitable replacement at any PC shop...