On your hard drive, open the worldpay module to see what files it contains. It is likely that the module may have over-written some of the core modules.
Via your FTP program, you must now REMOVE all the worldpay files, and if these files REPLACED a core file, then you must re-instate the core file.
Look also at the possibility that you initially FTP'd worldpay files to the wrong place(s).
In short, you are going to have to UNDO the upload of that module.
I don't know if the module made any changes to the database (probably not as all you have done thus far is FTP the files to the server - dbase changes only normally happen with payment modules when you INSTALL the module via the admin panel - which you can't access yet).





