Create a new folder on your hard drive and then copy the two files to the new folder.

If both the *.sdb and *.sdw have the same prefix filename, then they are probably from the same file and should work but it is possible the files are corrupted in some way. I doubt the problem would be in your firewall or antivirus.

Do you possibly have an old version of Access and if so, can you open a normal Access mdb file? If so, the problem is probably with the Simply file not the system.

Where did the files come from? Do the same copies work at the source?