JudgeJeffries - 1:26 am on May 25, 2012 (gmt 0)

I recently changed hosting for a very old website and suddenly its performing well again which it used to do in the past having slipped dramatically a few years ago to the extent that I had just about given up the ghost.
My question is whether or not a change in host could have made such a huge difference and what are the possible reasons for that difference. I had thought it may be due to a rival website being hosted on the same server and being given preference in the serps or perhaps a penalty on the server.
Any suggestions on this matter would be appreciated.