Singing to your records or Karaoke is a good idea to get a general feel of the process, but it doesn't really tell you if you can sing, because you KNOW how the song is supposed to go. The real trick is to sing to new melodies - create your own melody line for your vice, try different scales. If you don't know any musicians willing to play music for you to sing to, try to get some music without vocals - like jazz, though it might be hard to sing to Jazz at first because of the cord progressions, etc. If singing along to new music comes to you with ease and is fun, then hey, you can sing
!