There are a variety of reasons a writer falls into a rut that's difficult to climb out of.  More often than not, in my experience, it's because the writer finds him/herself:

• overloaded or overworked
  
• uninspired
• tired and/or hungry
• distracted
  
• pressured by deadlines

I don't know how others have done it, but here are the top 5 ways I've managed to detach myself from the rut I was in:

1. I would just get up from my work seat, away from the computer.  Take a coffee break, a shower, a walk, do a quick workout, have a massage, a nap...
   
2. I would read.  Reading gives me a shot of inspiration or a way to escape to some place and time when taking a real trip isn't an option.
3. I would play a couple of games. Just the short ones. My faves are word twist and bejewelled. It's a break from work, but not quite a break from the computer.
4. I'd buy myself something pretty or fabulous, or remind myself of how much I want to buy this pretty or fabulous item.
5. I'd force myself to do a chore I put off too long.  Maybe that was -- in the deep recesses of my subconsciousness, actually keeping me from focusing.

There.  Now back to work.