I spent ages reinstalling the FTDI drivers and going mad until I found this,
I originally had a 3.3v 8MHz pro mini that had worked well , I then got 3 more (clones) that did not, only when I retried the working one did I realise that all 3 new ones were bad .
After updating the bootloader using an arduino uno with the ardino as isp method as described here , I was able to fix all 3 easily.
Now I have the pro mini's all working with the latest FTDI driver (CDM_v2.12.00_WHQL_Certified) and can upload using arduino 1.6.4 IDE, on Windows 7 x64,
The clones had never been used except when try to upload for the first time, so I am sure I did not inadvertently set it to the wrong loader etc. My guess is that thy were possibly created with the wrong one (the 16Mhz 5v possibly ?).
So I guess the moral is don't buy the cheap clones unless you have a lot of spare time to track down these sort of issues.