I built a computer for a friend, using: Asus P4T533C motherboard TDK 40X CDRW Sony DDU621 DVDROM 512MB DDR RAM 2.26 GHz Pentium 4 All of a sudden, nothing is being detected. Only the floppy, but no hard drive, or CD Drives. I've tried switching cables, trying to detect only the hard drive, but still nothing happends. I think it's the motherboard but does anyone have any suggestions? He wants to bring it to a PC Repair Store but they charge $25 just to open the case. Anyone with ideas?

You're post is written in such a way as to suggest that everything was OK at some time recently. If so: and provided that nothing was changed in the configuration [HDD cables, Optical Disk cables] and all IDE devices went 'off the air', then it is fair to suggest that the IDE controller[s] or the chip have failed. Save some time and the possibility of further damage. Take it back to the shop where the MOBO was bought and have them inspect it: you'll either get the problem fixed or a new MOBO [which will be another fix].

IF it has been on the receiving end of a sharp surge up the power line i.e. from a poor mains switch connection - arc THEN it could have knocked out all your IDE devices. This happened to me once with THREE computers when the mains switch on the fusebox at the wall was faulty and was arcing every time something was turned on which drew a lot of juice at startup. Try to borrow another drive and stick it on the ide channel. If still no luck then it is either the motherboard or could even be the power supply!)

IDE cable are plug in right?red ligne on number one pin, i'm saying this because if your cable does not have the notch in the midile the mistake could be very easy to do.

Another thing is make sure that the power plug R-B-B-Y is plug in all the way.