Where did you create the vanity address? Did you have 2-factor set up? You don't need to throw out your comp but I wouldn't use it to store or send bitcoins unless you know its safe as you could have some keylogger malware.
OP where did you create your vanity address?
It's not the only option but it's very probably that was the weak point.
I recommend you using this app to store BTC for a long time:
https://bitcointalk.org/index.php?topic=811397.0