After a blunder from one of my admins, my site is completely messed up and I'll have to do a complete reinstall. Is there anyway I can do it and use my existing database?

Depends on what is wrong. Do you know if it is a file or database problem?

Anyway, for your information you can re-run install and it won't overwrite your existing tables--but I don't know if this will be an advantage to you if your database has problems. To run install upload your install folder and the original mainfile.php to your server.

If this does not work you will need to drop all your tables using phpadmin. You can also dump a backup of your database using phpadmin. In phpadmin you go to "Export", remember to "select all", and choose all the other options available like "insert" options.

After you you completely re-install XOOPS and a new database, and install your modules, you can use the "insert" data to salvage previous information for users and modules using phpadmin i.e.

INSERT INTO `xoops_users` etc etc.

This can be a bit tricky if you have not done it before though

Yup, managed to do all that. Curiously I now get the message "failed to open file" when I try to go into the admin menu.

that was quick..

Is that the complete message you are getting?

Is this after a complete fresh install? Sorry, I don't have enough information, what was your original problem?

I basically reinstalled XOOPS and managed to get all the dbase up and restored.

I know just get "failed to open file" when trying to log in to the admin area. Thats it, can't give any more info but thats all it tells me

I see,

to manually switch on debug see

http://wiki.xoops.org/wakka.php?wakka=FAQDebug

I would also check your Cache folder and template_c folder has high enough permissions. It could be you need to delete adminmenu.php in the cache folder to allow XOOPS to rebuild the admin menu. (I am guessing though, I would try a debug first)