Hi Ben,
Thank you for responding, yes it is a strange one. I spent 2 evenings just scanning the forum to see if my issue had occurred previously with other users prior to posting up. I didn't find any.
1. Yes, the files play perfectly in both Windows Media player and Winamp Player. Eash file shows the correct full length of each track.
2. The C drive currently has 99.6 GB available (out of 232 GB), my D Drive which is my new storage of music has 56.8 GB (out of 232 GB) and finally my k drive has 236 GB (out of 372 GB) available. I have tried playing random files from each drive without any problems, then the same files were then loaded up into wavepad and still only loading up to a maximum lenght of 7:51.280. The files were both tried ticked Read Only and unticked.
The same files were then converted using NCH Switch (I have tried a variety of formats including Wav & Flac), each loading fully and the file sizes in most cases being larger than the MP3 format. For example, I'll call it Track #1, the length is 8:52 mins., as a 320kbps MP3 file it is 20.3MB, as a Wav file it is 89.6MB, but the larger file loads up fully. I then converted the same wav file back to an MP3 but as a 128kbps file with a size this time of 8.13MB and again only a part loaded.
The issue therefore isn't file size related, but the something to do with the MP3 format. This was why I downloaded the up-to-date version in case the original crash that happened, might have affected the MP3 algorithm in my older version.
I will pm you with my email, I use both We Transfer & Dropbox. At the moment I'm converting longer files to wav format prior to editing but I'm hoping for a solution. I wonder would deleting the complete programme and then reloading make a difference? I wasn't sure if the Registration code sent upon purchase would still be active? Otherwise paying for software again and finding the same fault occuring would be hard to swallow 
Regards
Twync