Although you should never let any HPLC column dry out, your column is probably not ruined.
However, It could take days to get it restored when conditioning it with your mobile phase. If there is air in the column, give it a few hours of slow flow rate of your mobile phase or use isopropanol (IPA) to purge the air out of the column. Then re-condition it according the original instructions.
If the low retention is not fixed by the re-conditioning, it could be a method development issue. Just as a point of reference, check that you are not starting with 100% A because if you are looking for hydrophilic analytes, they will not retain under reversed phase (RP) conditions. Make sure your analytes are ionized in solution before injection, that your mobile phase solvent A has either acid or base (but still within the pH range of the column) in it, solvent B is acetonitrile and 5% DI water with the acid or base you have in solvent A and that the column is conditioned according the instructions it came with.
