when i click install nothing shows up

[mc12345678]

i redownloaded zen cart from the server and overwritten the those files. i tried going back to the express check out and face the same issue..

should i install an earlier version of zen cart?

No, an earlier version of ZC does not need to be installed. Are there extra files in that same directory (includes/modules/payments) as compared to a stock ZC 1.5.1 file set? Are there files in the override directory includes/modules/YOUR_TEMPLATE/payments that are different than the other directory above? (There may be a valid reason that differences exist, so blindly overwriting is not always a good idea.)