Don't know if you have the recording gear or not, but what I usually do when I get sick & tired of working on a song is drop in a bunch of random loops from various sources. Like, I'll take the 48 track tune or whatever it is and just go searching around on my hard drives for loops at the same BPM. Then turn everything down to zero and mix and match stuff until something more interesting happens. I did that on a song called "Neon Lies" ages ago. It was going nowhere for over 2 years. One day I just grabbed a random drum loop, dropped it in and it fit in perfectly. Then that loop spurred me on to add some other stuff on top of it.

If you have stuff recorded in MIDI, try substituting different midi instruments for the ones you usually use. Like, I'll drop strings in place of synth or use the midi drum track to trigger a synth.

Don't know what to do if you don't have recording equipment though except maybe just put it to one side for a few months and come back at it with a fresh perspective later on.