I used to be able to write really good original songs on guitar. Over the last year I completley lost that ability. The last good song I wrote on guitar was over 6 months ago. Now the only thing I'm able to do is make good ambient music. I would appriciate it if someone could give me some ideas to stop this writers block or maybe tell me about a few bands ( doesn't have to be metal) that would inspire me.

I recently overcame a writers block myself.

Just go on a listening spree, spend a whole day just constantly uncovering new bands and listening to old favorites, just do this non stop.

Then, the next day, see if you don't end up with some inspiration.

Rather vague advice, I know, but it worked for me a lot. I'm writing better stuff now than ever before.

Explore jazz and classical. There's enough incredible music there to give you inspiration for a lifetime.

Shostakovich, Tchaikovsky, and Wagner are all great.

Thanks for the advice. I recently started listening to classical and like it alot. I was wondering what you would recommend for jazz?

Aside from whats already been suggested, which are very helpful pieces of advice btw, heres my two cents. I've had this problem before, it usually occurs whenever i pick up the guitar and go into playing with a mentality of "i'm going to write some good riffs/a new song." By doing this you are putting pressure on yourself to write well, and you end up playing utter shit. Don't have any expectations, just let things flow and come naturally.

Sorry to butt in on MattP's response

Personally I prefer jazz fusion, so I like listening to artists such as Alan Holdsworth and Weather Report.

But in general if I have a writer's block, I just seek inspiration from the projects of other musicians (of any genre) - it spurs me on.

I think I'll way in as well. For Jazz Fusion you can't forget Return to Forever. Maybe try some Marcus Miller or Victor Wooten (no I'm not black, these guys are just amazing).

When I have writers block I just listen to a lot of progressive music and video game music. I also often just take a short break from music. I free my mind a little by exploring my other hobbies that are much less demanding.
Plus, I agree that you shouldn't put expectations on yourself to write a song. I really hope you get past your writers block, good luck.