Oscommerce 2.3 Categories / Products repair

We have two sites based on oscommerce 2.3 , on the front end Categories / Products are fine however when you login on admin and click the page at first it shows but blank then goes to page cant be displayed, there was a hacvk on the site a little while back however the issue does not seem to be related to this , we have replaced [login to view URL] from the original source however this has not resolved the issue, we would also be interested in any add ons that can be advised, example site speed up and one click checkout, lastly we would also like site maps . Please contact us in you have any more questions, time scale of 1-4 weeks however we want to avoid down time of the site. other projects make also come from lthis.