A few basics Valli, I'm not trying to be patronising (like phoning your ISP for them to ask if the router is switched on) but its sometimes a simple oversight on getting P99 started.
1. Have you installed EQ Titanium? (ie - you're not trying to connect using your EQ Live folder, right?)
2. Are you using the launcher? (downloadable
here) - running the launcher with your installed folder specified and selected "Project 1999" will just double check your files are all okay and good to go.
3. Have you tried disabling your firewall and logging in? Hyper-sensitive firewalls can often block programs from running...if you can log in ok without the firewall on, it might be a case of adjusting its settings, or allowing the EXE file to run.
Can you say some more about the screen flashing? That's a weird one, could be a graphics card issue?