I bought a Sega dreamcast, and house of the dead two. I can't seem to get either guns or standard controllers to work on the game.It works fine with other games.

SOURCE: Sega Master System Cartridge Issues

I found out what was wrong. The all of the solder connections where the cartridge slot pins meet the board were broken. I was able to verify that this was the issue by pressing the connections together while trying to boot up with a cartridge and it working. I will just need to get a fine tip for my soldering iron and some really small gauge solder.

SOURCE: Dreamcast Loading problem

you can get disks relayered at game stores.
there was a long period where this happened to me.
some games worked for a while, some didnt.
its the dreamcast.
you might wanna get anew power cable or just clear out the dust because that is the main problem with the dreamcast.
try playing with the console upside down
it sounds crazy but it worked for me.

SOURCE: sega dreamcast wont play games

Clean the laser using a dry q-tip with a circular motion.

If that doesn't work then watch this video.