Black screen is popular problem and there are many ways to fix it:
1) Make sure you closed all firewalls;
2) If you can't close firewall go to settings and allow Fallout Tatics to connect at all;
3) There is a firewall in Windows XP, you need to turn it off... go to your connection settings and find it there;
4) Make sure your FoT ports are open (read instruction), if not then open them with proxy or contact ur internet operator;
5) Make sure you got 1.27 patch;
6) Make sure your Fallout Tactics works on singleplayer;
7) Try to connect by IP... if it works then its GSA fault... reinstall it and change some things in options/games/, it usually helps;
8) If you got something like celeron 300 and 64mb ram then you have to wait 1-4 minutes to connect game;
9) If it didn't help, then change your internet operator

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Im sure it will help...