Won't shoot with flash on or on auto

The hand signal means you need to hold the camera very steady, or use a tripod when shooting the photo. This is normal in auto mode, when shooting in low light conditions, as the exposure times are longer. Also, shooting a moving object will become blurred, but if nothing is moving, and the camera is held still, there should be no distortions.

The flash may be broken.
If not these are the flash settings on the camera in case a different flash mode has been set accidently.

Set the mode dial to [camera icon], and press [up arrow] on the control button repeatedly to select a flash mode.

The flash mode has the following features.
No indicator (Auto):
The camera decides to use the flash based on lighting
conditions. The flash will be used when
there is not enough light or when shooting a
subject against a light source.

(Forced flash):
The flash will be used regardless of the amount of ambient light.

(Slow synchro):
The flash will be used regardless of the amount of ambient
light. In this mode, the shutter speed is
slower under dark conditions, so you can
clearly shoot a background that is out of the flash-lit area.

(No flash):
The flash will not be used.

The build in flash, will be useful within several meters (15 to 20 feet) if it is really dark.
Your camera should be capable of taking pictures in poor light conditions. Try to shoot in automatic mode. The mode dail to AUTO. (green camera symbol). Then view the picture with info. There you can see the ISO, Aperture and shutter time. From there you can experiment for darker or lighter pictures. For this you can choose M, A,S or P.
In each of these modes, you can use the following steps.
On top of the camera, close to the shutter release button you see a little knob with a +/- sign. If you press that button, you should see a 0.
If you see a - figure, this means the picture you shoot all be darker than normal. If you see a + sign with a figure it means the picture will be brighter. While pressing that button and turning the command dail, you can choose -3 to +3 EV. That is much darker and much brighter.
If you shoot many pictures in bad light conditions, you could buy an external flash. A Nikon flash will work very good and automatic, with your camera, because camera and flash will communicate and help each other to make better pictures. Cheaper external flashes can work too, but most of the time you must change settings manual on the flash. Never use old flashes, that were build for analog cameras. They sometimes switch with a voltage higher than your camera can handle. The camera can be damaged by such a flash.

Hello: The flashing engine light means there is a misfire (one or more cylinders not firing) Take it to Auto Zone, Advance Auto or O'Riely Auto parts stores, they can read the code and may not charge you. There are several reasons for a misfire: Fouled spark plug/bad spark plug, bad ignition wire. bad coil, bad ignition module, bad injector, bad engine control module. There is no way over the internet you can determine the exact cause. This condition will have to be found with hands on trouble shooting.

on the side of the lens check to be sure it is set to auto and not manual.

Automatic settings are not useful in all conditions. The built in flash is not good over 20 ft. Under low light conditions, an external flash is better option, but it costs additional too. Remember that shooting under low light conditions is always a difficult task. By the way, I don't know about such common problem in Canon XTi

Quick solution: enable the "auto ISO" setting in the menus. This will automatically recognize low-light conditions, and adjust the ISO accordingly.

What is the best situation to use each of the shooting modes? The shooting modes are described as follows: Program Auto (Factory default setting) Program Auto mode is used for regular photography. The camera automatically makes the settings for natural color balance. Other functions, such as the flash mode and metering, can be adjusted manually. Portrait Portrait mode is suitable for taking a portrait-style picture of a person. The camera automatically sets the optimal shooting conditions. Landscape + Portrait Landscape + Portrait mode is suitable for taking photos which include both your subject and the landscape. The camera automatically sets the optimal shooting conditions. Landscape Landscape mode is suitable for taking pictures of landscapes and other outdoor scenes. The camera automatically sets the optimal shooting conditions. Night scene Night scene mode is suitable for shooting pictures in the evening or at night. The camera sets a slower shutter speed than is used in normal shooting. If you take a picture of a street at night in any other mode, the lack of brightness will result in a dark picture with only dots of light showing. In this mode, the true appearance of the street is captured. The camera automatically sets the optimal shooting conditions. If you use the flash, you can take pictures of both your subject and the night background. Self-portrait Self-portrait mode enables you to take a picture of yourself while holding the camera. Point the lens towards yourself, and the focus will be locked on you. The camera automatically sets the optimal shooting conditions. The zoom is fixed in the wide position and cannot be changed. QuickTime Movie QuickTime Movie mode lets you record movies with sound. The focus and zoom are locked. If the distance to the subject changes, the focus may be compromised.

The Shooting modes are as follows: PROGRAM AUTO (Factory default setting) Used for regular photography. The camera automatically makes the settings for natural color balance. Other functions, such as the flash mode and metering, can be adjusted manually. Portrait Suitable for taking a portrait-style shot of a person. The camera automatically sets the optimal shooting conditions. Landscape Suitable for taking photos of landscapes and other outdoor scenes. The camera automatically sets the optimal shooting conditions. Night scene Suitable for shooting pictures in the evening or at night. The camera sets a slower shutter speed than is used in normal shooting. If you take a picture of a street at night in any other mode, the lack of brightness will result in a dark picture with only dots of light showing. In this mode, the true appearance of the street is captured. The camera automatically sets the optimal shooting conditions. If you use the flash, you can take pictures of both the subject and the background. Self Portrait Enables you to take a picture of yourself while holding the camera. Point the lens towards yourself and the focus will be locked on you. The camera automatically sets the optimal shooting conditions. The zoom is fixed in the Wide position and cannot be changed

The shooting modes are described as follows: PROGRAM AUTO (Factory default setting) Program Auto mode is used for regular photography. The camera automatically makes the settings for natural color balance. Other functions, such as the flash mode and metering, can be adjusted manually. Portrait Portrait mode is suitable for taking a portrait-style picture of a person. The camera automatically sets the optimal shooting conditions. Landscape Landscape mode is suitable for taking pictures of landscapes and other outdoor scenes. The camera automatically sets the optimal shooting conditions. Night scene Night scene mode is suitable for shooting pictures in the evening or at night. The camera sets a slower shutter speed than is used in normal shooting. If you take a picture of a street at night in any other mode, the lack of brightness will result in a dark picture with only dots of light showing. In this mode, the true appearance of the street is captured. The camera automatically sets the optimal shooting conditions. If you use the flash, you can take pictures of both your subject and the night background. Self-portrait Self-portrait mode enables you to take a picture of yourself while holding the camera. Point the lens towards yourself, and the focus will be locked on you. The camera automatically sets the optimal shooting conditions. The zoom is fixed in the wide position and cannot be changed. QuickTime Movie QuickTime Movie mode lets you record movies. The focus and zoom are locked. If the distance to the subject changes, the focus may be compromised.