Check the SMTP outgoing mail server setting and make sure it matches what you use on your notebook- that's probably the outgoing mail problem.
You might be running into memory problems because too many programs are running. Unfortunately Microsoft doesn't like the idea of exiting programs but rather minimizes them. Though the PDA should automatically start killing apps if memory gets too low, it doesn't always work too well. Try downloading and installing a free app called Magic Button. With this app, when you tap on the close box it will exit the program rather than minimizing it.
For that dreaded Guest issue... have you installed any new AntiVirus or firewall software? Sometimes those get in the way. If you use Firewall software, make sure port 900 is open for ActiveSync or the PDA might be seen only as Guest.