My first thought is that you'll be needing more memory. If a disk based game requires 1MB of ram (most of them), then those games are definitely not going to work on a 512kb machine. Also, it will either freeze or crash because those games were meant for a machine with 1MB and upwards, and were programmed assuming this configuration.
You can buy cheap memory expansions from e-bay though that will slot into the trapdoor on the underside of your A500 and give you 1MB in total. It will be called a 512k chip memory expansion.
Another thought is that those HD disks you are using aren't liked an awful lot by your DD disk drive. Try writing the same ADF to the same disk 2 or 3 times in succession.
Another thought is that your disk drive heads may be in need of cleaning.
Another thought is your ROM. You have version 1.3....some games may require version 2.0 with 1MB (ie an A500+). Again, you can purchase 2.0 ROMS / ROM switcher for your A500 from ebay.
Hope to have been some help.
