|"dell gx620- micro footprint"|
Do you mean Ultra Small Form Factor?
"if i use a usb to sata adapter will it boot from usb"
No, & you don't need it to. Just leave your current HDD connected & put the new HDD in the external USB doc. You will have to partition & format it, then boot off the CD to clone the contents. If you didn't get a disc with your new HDD, go to the manufacturer's website & download.
"i don't have sp 3 because running good shut the hood logic"
More like dumb logic. Do you ever update drivers? Do you update your antivirus software? Why would you if they're "running good"?