Canon rebel xti focus issues

Just a thought - are your Image Stabilizer and Auto Focus switches On or Off?
Might be worth experimenting with them.
Otherwise, sorry, can't help.
May be necessary to contact your vendor.

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

Check the AF/MF switch over the lens left side. Should be on AF to let the camera focus by itself. If not, you have to manually focus using the focusing ring.

If the camera is in AF and still no focusing, considere to carry your camera for service.

I am having the same problem. I bought a Tamron zoom lens as an add on. This lens costs more than the camera and yet images are not as sharp as i would expect from such a highly touted camera. My Kodak Z740 point and shoot gives sharper prints. This is very frustrating. I bought Rebel for Dummies and still am having the same problem. Very frustrating

You have your own answer - the lens is damaged, probably beyond economic repair.

What are the lens specifications ? Try raising this query with the canon customer service.

On the back of the camera to the Right of the LCD there is a up-down-left-right-center switch. push the up one. (Labeled ISO) then use the same selector switch to select the ISO you want and then press the shutter half way down. If you are shooting in a low light situation, the auto focus sometimes will not work. Change the switch on the lens from AF to MF and focus manually.

this does not seem to be like a problem in settings

please use a different lens and try the same

if it is an auto focus lens that works on one eos camera, it should work on almost all of them. the only known exception is that some high end extenders will not fit the eos1dmarkII as it protrudes into the opening too far.
but a good rule is that if it fits without any obstruction issues, it should work. try cleaning contacts on the lens and camera body. if that doesn't fix it, talk to Tamron. you can use it manually, but will not be as easy and you would get less predictable results.

my suggestion is to always go with lens from camera maker.

sounds like there is an issue with the tamron lens. not the camera.
good luck
mark