Mame is in constant development. It currently has a cycle of four weeks between updates (excluding major breakages). These updates can contain bug fixes, new systems and updated software lists. The problem is that these updates can seem to "break" systems that have worked before. However, this is not always the case and a simple rom file update can sort most of the problems. Please don't get confused with roms and software. A rom file is an image of a chip from an original circuit board and software is loaded from media such as floppy disks, cd-roms or hard disks. To keep things simple, all the rom files for a system are zipped into one file and are given the relevant system name. Most arcade machines and computer systems will run with just these files but some also require software images as well.
Firstly, you'll need to download the latest version and extract it over the old one. There is a link to the Mame homepage in the menu at the top of the page. Just follow the Mame Installation page and when it asks you to overwrite any files, answer Yes. This shouldn't cause any problems with the general running of Mame however, updated systems may not work because some of your roms will be wrong. You'll possibly get an error like this...
File Missing Error Message
The most common problem when Mame has an update is caused when incorrect or damaged roms are replaced with good ones. If you find that a system that was working, doesn't run any more, you might want to verify that all the files are there. In the user interface, you will get the message below. If you use the command line then you'll get the message above.
File Missing Error Message
To fix this error you just need to re-download the whole system rom zipfile. There are several rom sites on the internet which host the updated rom files. Google is your friend there. The Pleasuredome site can also be a good place to get updates as they host an update torrent which has zipfiles of all of the changed systems in it. The link for Pleasuredome is in the menu at the top of the page.
If you want to just update the file, then you can find the rom you need and drop the un-compressed file over the relevant zipfile and it will replace the damaged rom. To find the file that is incorrect or missing then you will need to use the command line to get Mame to show the rom audit. Open a command prompt and use this command replacing <system> with the system name you want to check.
005 Error Message
The list generated will give you an idea of any wrong or missing files in the zipfile. If the rom is marked as "NEEDS REDUMP", there is very little you can do about it until the physical rom is redumped. Normally these files will not show as missing. If the missing file ends in
.chd then you are missing the CHD image file required to run the system. You will need to get this file for the system to run. You can find more information on CHD files on the About Roms/CHDS page.
Any missing files or ones shown as incorrect will need to be replaced. You could use Google to search for the files. There are a lot of sites where you can get them from. When you have them, just drop them over the zipped rom file and the new roms will be added. Now if you run the verify command again you shouild see something like this...
005 O.K. Message
If the rom file looks right and you still get an error then it could be caused by a missing or updated BIOS file. BIOS files are used by some systems to hold settings and language information which meant that systems could be sent worldwide without major version changes for each country. For example Metal Slug is a NEO-GEO game and requires neogeo.zip to be in the roms folder as well as mslug.zip. To fix this issue just re-download the BIOS file.
If you are 100% sure that all the files are right and you still cannot run a system that ran perfectly before you updated Mame, then you may need to delete the nvram file for it. These files contain information from the onboard memory found on a systems main circuit board. If the chips on the board have changed, then the memory will be not compatible anymore. To delete this file you will need to open the
C:\Mame\nvram folder and delete the folder that matches the name of the system that your are trying to run.
There are programs out there that can help you manage rom files and help you fix a lot of the issues above. I'd personally recommend CLRMame as a good rom manager.