After cleaning a very dirty pc for a friend, the pc will not boot.  It begins, the fans run for about 1 minute then stop.  Only power unit fan continues to run.  There are no BEEPS, hd is running, cd and dvd roms are powered, but no video at all.  Switched to another video CARD and same thing.  I removed and replaced RAM and CPU. I am stuck and would appreciate help.  Thanx ahead of time.Did you suck out any jumpers? Seen this before where an important jumper gets sucked out and you have to then verify all jumpers are where they need to be.... On another NOTE I also seen where a person killed their motherboard by vacuuming and the vacuum acted like a Van de Graaff and a high voltage static DISCHARGE happens between the aluminum  tube of the vacuum hose and a chip inside the computer.

Hoping its just a jumper sucked up!   Also double check all connections to the motherboard and various components.
Is the 4/8 pin aux power connector plugged in? Caught me out many a time.1) When you say you "cleaned it out" we're assuming you mean you cleared the dust from inside the case. If you mean something else please explain.

2) Is there anything at all on the display or is it completely black?Good evening nurri and welcome to CH

Just like some of the other posts some things to check?

#1... I am assuming that when you cleaned out the PC you are referring too "DUST" and not software / applications?
#2... You say that you reseated the memory and CPU but did you try re-seating the "Video card" if this PC has a add on card?
#3... What MODEL PC so if a "jumper" did get sucked up or blown away during the cleaning if we know the model we may be able to tell you where to look for the jumpers!
#4... if there is a add on "video card" is there a plug at the end of the card and if so is is plugged in?
#5... Is the 20 / 24 pin ATX connector seated and locked in place on the MoBo?
#6... Is there any extra 4 pin connectors to the MoBo and if so are they plugged in? (a lot of 4 pin plugs have 2 yellow and 2 black wires) but that will very on PS companies also.

Hopefully with all the posts in here you do get back up and running and please come back and let us know how you make out, Mike    I have encountered a similar problem, that is if this is not dealing with software.

The jumper i know to cause the most problems is the BIOS mode select jumper, usually located near the CMOS battery. This is three pins up from the mother-board, and when the jumper is not in either "Normal" or "Config" mode, the computer usually displays similar symptoms to what you describe. At least this is my experience across several desktop computer types.

Either way, i hope you find the jumper you need. I always keep some hanging around in the event things like this would happen. May I suggest we wait to hear from the OP to find out what the problem actually is?