Your turntable could have a preamp on board but its very unlikely. I'd check using the model number, also I think its only Stanton DJ decks that have a line level output. What you need to do is invest in a phono preamp like
this or find an old Hi-Fi amp that has a "phono" input that is for a record deck. Then you take the output of your 'table and input it in the preamp/Hi-Fi amp and then take take the output of that and put it into your mixer/mpc etc. If I'm correct, the reason your signal sounds weak is because vinyl is mastered through special RIAA EQ curves that make the sound possible to cut to vinyl so that the needle doesn't jump everywhere. To get a proper sound you need a preamp to reverse the EQ and amplify the signal (which is why you should never plug a CD player into a "phono" input because you'll blow your amp). All DJ mixers come with this as standard because they all need to cater for vinyl but standard recording mixers do not because they're designed for line-level signals.
Right, hope that clears everything up...
Oh yeh and smoove is right speakers help...