My canon eos rebel xt 350d wont focus

Sound like a broken ribbon cable in the lens. Needs to be replaced but get a quote as it may be cheaper to replace the lens with a secondhand one.

I think this EF-S 18-55mm Lens http://www.bobatkins.com/photography/reviews/18-55.html will suit for your Canon EOS 350D .

Sorry but you need to take the lens and/or camera in for service....could be expensive.

Clean the contacts on the camera body and lens where they meet with a cotton swab lightly dampened with rubbing alcohol.

There is a minimal focusing distance for all lenses. If you move closer to the subject than that distance then the camera won't focus on it. Check you lens manual for minimal focusing distance. It is 11 inches for Canon EF-S 18-55mm f/3.5-5.6 USM, for example.

Try going to Canon's website and updating your drivers AND you firmware.

Try a different lens just to check out the lens focus sensor. or put it in manual focus.

part of the electronic switching board is damaged and needs replacing

Move the switch on the lens from MF to AF.

The auto focus setting is in he lens and not the camera body

low light means the shutter stays open longer to capture the image.   Try changing exposure settings.