there usually is some sort of administrator account, but you will have to know if there's a password created for it, try it, with a blank password.
if not, you can try logging into that computer with the old account, and create a new account. DO NOT ACCESS any banks or sensitive information from that computer. The general rule is that if you get infected by a virus, you should change your banking passwords as soon as you can, just to be sure. sometimes they use password stealing software so better be safe than sorry.
if you have an external USB drive you can plug that in to the infected computer and offload pictures and any other files that you want to preserve. If you don't have one, check out Best buy and future shop, they have them for some great pricing now, (500 Gb for about $170 or so). You should use these as a backup device, and not storage.