Take it off the car. Dismantle the electric part. If there is any sign of a burnt out motor buy a new wiper unit.
If not it might be worth trying to get your old one working. Remove the "circlip" below the splined end of the shaft. Soak it in penetrating oil or bung it all in a bucket of diesel! after a couple of days give the shaft a couple of taps (lightly) with a hammer to get it moving then use a shifter on the other end of the shaft to keep it moving. If you can get it moving freely then it is just a case of re-assembly.
It worked for me and saved nearly £100. If you buy a second hand one I would recommend stripping it down to make sure that it is well lubricated. It is nearly always the shaft that siezes.
"When you sit in a Focus RS or a Golf R32 it’s like sitting in a commercial for Lynx aftershave. When you sit in an 147 GTA it’s like sitting in a Venetian’s hand-made suitcase." J.Clarkson 2003.
Current fleet: 156 Sportwagon jtd 16V (facelift) 2.4 Spider, Leon Cupra SC
Projects: Spider S4, Matra Murena 2.2