SB_usb_log

What is your question exactly?

1. Is it whether a file named SB_usb_log is malware? And isn't the file name really SB_usb_log.txt ?
2. Or is it whether a slow PC means you have malware?

For 1, it is not malware. It is probably relate to a Motorola USB Driver Removal Utility You could just load the file into notepad and probably get more info on what it is.

For 2, most frequently slow PCs are cause by what you are running and not by malware. But you would have to be more specific and describe exactly what operations are slow and is it always like that. Also is it slow in safe boot mode.

 

In most cases slow boot ups are due to what you have installed and are running and that is where you should look. Actually Norton is a major contributor to PC slow downs especially if what you have installed is one of the Internet Security Suites. If you want to know if it is your problem, you need to uninstall it completely. Do not make the mistake of just trying to disable it in MSconfig which never has the same effect (especially if you don't disable all startup as well as all services).

Your PC really as an inadequate amount of RAM for the way applications work these days. The minimum I would suggest is 1 GB.

You really should test to see how your PC boots in safe mode and let me know. While I could have you run the full READ & RUN ME sticky procedure to check for malware, I tend to doubt that it is your main problem even though it is possible that you have some malware. It's your decision if you would like to do this check, but if your PC is fine after initial startup, it is most likely due to the applications you have loading at startup. As stated, Norton is a big problem and ZoneAlarm (especially newer versions) also causes slow downs on many PC especially ones with inadequate amounts of RAM.