reinstallation of ubuntu 14.04 failure

I have ubuntu 14.04 installed on в 500 Великобритания external hard disk. It - 20 Великобритания / partition, 5 Великобритания partition for linux swap and 475 Великобритания / home partition. Because of problems I tried reinstallation of ubuntu 14.04 from live usb on the 20 Великобритания partition, opting for formatting only that partition. Everything went умер till nearly the end, "update grub" operation which failed. I was given an option to продолжите without boot-loader which I declined. I tried to ширма the reinstallation which was declared в failure. Now fdisk шоу my hard disk to be 500 Великобритания but says it does not contain в valid partition table. Gparted шоу only 475 Великобритания "unallocated" space. I want to get back my датирует on/home partition and also to reinstall ubuntu 14.04 again. How do I go about it? After few hours: OK. I have got my partitions back using testdisk. All my восходит is in tact. However I still need to reinstall ubuntu 14.04. How shall I proceed and any ты разрабатываешь of what to do so that there is not another failure of reinstallation?