I had something quirky happen today, I was doing a database restore from Management Studio 2005. I selected my backup file, then went to the options folder, selected overwrite the existing database. Now here's my problem, I click the ellipsis to select the file location, I navigate to the folder where the .mdf file is located and I cannot see the mdf files I logged into the server to verify that the files were at the location I had specified and they were. Why can I not see the mdf files? The .ldf files are on another drive and I can see them!
Never seen that one myself sorry. I would try refreshing the view. Then I'd log off & log back on. Then I'd try restarting SSMS. If none of that worked, I'd go and check security to validate something hasn't changed in my persmissions (those are the permissions you'd be browsing under, not the servers) if I had previously been able to see stuff. Also, check silly things like that the extension said what you thought it said when you went to that directory (was it MDF or NDF, that sort of thing). If it's none of those, I'd file a bug with Connect.
My bet is that you copied the MDF files to the directory and somehow managed to do that in a way that the account that SQL Server is running under did not have access to the files. Check the security on the files themselves to make sure that SQL Server's service account has full access.
were you using SSMS on a different computer from where you were doing the restore? The folders you navigate in the wizard are the server folders, not local drives. Are they standard file types - mdf, ldf, ndf or something else? Are permissions OK - did you open SSMS with SQL or Windows Auth? Does the SQL Service account have permission? Sorry if its repeats/stuff you have tried already ... this is a weird one!