WRITERS BLOCK!

Play some different style of music. Learn some classical shit especially. Thats a great way of getting riff ideas.
Learn some new scales and mess around making riffs out of the pattern.
Listen to some new stuff that you dont normally listen to.
Write "sections" complete with drums/bass/guitar instead of just riffs.
Try playing some cleaner stuff like Opeth style picking.
Take a different approach. Lay down some chords, write a melody and then combine the two into a riff.
Write a chord progression you like and make a riff out of it.
 
Everything that shred said. You could try to write some drumpatterns first and jam around to them, too. That's the way I write all of my stuff. I play in a progressiv hardcore/metal band (no metalcore;)) and I found a lot of inspiration from movie soundtracks lately (I stole a riff that's in the soundtrack of "28 day later"... no on purpose:))
 
i think my problem is that i've been mixing alot of DubStep and BreakCore songs lately that my mind is stuck in programming mode, damn dj work, i knew it would infect me
 
This may not work since you say you've been doing a lot of DJ work lately, but I was gonna say to stay away from your regular element for a while, as in don't listen to metal for a while, maybe a couple weeks (might be tough, I know) and more importantly don't TRY to write anything. Maybe practice some basic guitar stuff to keep from getting rusty if you're worried about that happening, but seriously stay away from metal. Meanwhile don't be afraid to be inspired by everything and anything, and soak things up like a sponge, even if its not your preferred style of music. Study the details and try to discover the appeal if it's not immediately apparent.

After a week or two you'll be craving metal so bad you can sort of rediscover what you love about it and hopefully be massively inspired by the same stuff you've heard plenty of times before. Kind of like hitting a reset switch. Only not as fast, haha.

Just like when you've been away from your girl for a long time, then when you hook up again its like rediscovering her vagine all over again and you plow that shit with a renewed sense of passion and fury. Songwriting is like that sometimes.
 
For me, recording EVERYTHING you come up with works. Even if you know that the riff sucks, just record it. It is much easier to discard recorded ideas later than work with nothing at all! Try adding a harmony part or a lead part to that riff, see if it becomes more than the sum of its parts.
 
For me the best ideas come when i'm not supposed to write/play music, which is when i'm outside going to work or to someplace (then i have to try to remember the idea and write it on guitar pro afterwise).

If i "force" myself to write riffs, it will always sound forced and phoney.