When you say it 'stopped working' what exactly happens? Does the app boot up successfully? When it goes through the process of searching for your PC does it 'find it'? If you try to 'log in' to your PC once it's been found, does that process succeed?
Send us some more detailed information and we'll try and help. I've used Splashtop for some time now and not had any problems, but you might try powering your iPad completely off (hold down the Power button until the slider control appears) and then on again - that fixes a whole load of 'issues'.
Tim