Multiwavelength observations of a prominence eruption provide an opportunity to uncover the physical mechanism of the triggering and the evolution process of the eruption. In this paper, we investigate a prominence that erupted on 2012 October 14, recorded in H alpha, EUV, and X-ray wavelengths. The process of the eruption gives evidence for the existence of a helical magnetic structure showing the twist converting to writhe. The estimated twist is similar to 6 pi (three turns), exceeding the threshold of the kink instability. The rising plasma reached a high speed of 228 km s(-1), followed by a sudden rapid acceleration of 2715 m s(-2), and was synchronous with a solar flare. Co-spatial cusp-shaped structures were observed in both 131 and 94 angstrom images from the Atmospheric Imaging Assembly, signifying the location of the magnetic reconnection. The erupted flux rope finally underwent a deceleration with a maximum value of 391 m s(-2), which is larger than the freefall acceleration on the Sun (273 m s(-2)), suggesting that the eruption finally failed, possibly due to an inward magnetic tension force.