My Mac is suddenly acting up

I know Macs don't get viruses but it seems like something weird is happening.

1.First of all, it freezes a few times a day, forcing me to power down because it goest completely dead.

2. Then, suddenlly we can't have two devices using our Time Capsule at the same time. That's new.

3. Now I see something in system preferences called ZTEUSB Modem- no idea how that got there

4. Something to do with Canon displays a new dialogue screen each time and asks about scanning- something i never do. So where is this screen coming from- and why is it asking this?

5. suddenly getting dialogue boxes about Bluetooth- didn't even know computer had bluetooth. And don't know why or how it has been activated

All these weird happenings leads me to think there is a fundamental problem in the system. I do't know where to begin. Do you think something infected my system/