Nikon D3100 video shooting problem?

1) I have a problem with aperture its not going below 5.3
2) Whenever I shoot a video its not recording more than 10min's

1) Your 18-55 is not a constant-aperture lens. You can shoot @ 3.5 @ 18 and as you zoom in the maximum aperture becomes smaller.

2) Yup, the 3100 has a 10-minute limit to prevent the sensor from overheating

If you mainly record video, trade the 3100 for an actual camcorder. Despite popular belief, DSLRs are not replacements for actual camcorders and do not offer better video quality than actual camcorders.

1) You likely are using the kit lens. It has a variable maximum aperture depending on the focal length. Its maximum aperture is f/3.5 at 18mm focal length, and gradually changes to f/5.6 at 55mm.

Try a shorter focal length (zoom out), then lower aperture values should become available.

2) That's to protect the sensor from overheating. This is normal, there's nothing one can do about it (except buying a dedicated camcorder).