Which firmware are you using? Ar you using DVK or custom board? Are you downloading hex to FX2LP RA, or are you trying I2C boot? Please clarify these.
Also, please elaborate your statement "but when i move to windows 8 something goes wrong". What is the bahaviour seen. Does it show up as any unkown devcie in the devcie manager? If so please check and let us know the VID/PID with which it enumerates. If it doesn't what is the behaviour seen?