If its the same fault that I had it was a broken cable. Needed complete mechanism and cost me £270.00.
Sorry to be the bearer of bad news
Oh why Oh why don't you guys shop around, I got a brand new unit for £100 and a guy does repairs for £40 (see
item180076856291 ) and it's a fairly easy job to fix. Search the forum and you will see loads of info on window mechs.