I am on Windows XP

I have tried to load a upgraded Firefox After doing this I could not run firefox I click on the short cut and on firefox in the strat programe mode. I was going to delete firefox and reload but I go to remove hard and soft were click on firefox to delete it and it says close firefox to perform this request. I want to close firefox but can not can you tell me how I close firefox as I can not get on to firefox as it will not open. Thanks Tony