Hello,
the only driver you should use is the Yamaha Steinberg one. Make sure you have the latest installed:
http://www.steinberg.net/en/support/downloads/downloads_ci2.html
Go to Cubase → Devices → Device setup → Yamaha Steinberg → Control panel and see if it helps to raise the buffer size. You’re computer specs are a bit on the low side so you might need to yank it up a bit. A new computer would probably solve all your problems (Or maybe not all but everything related CI2 and Cubase 
).
See this excellent thread here for more troubleshooting advice:
Cheers!