This is really frustrating. I'd like to return the hardware except that I bought a starter kit and it isn't the fault of that vendor.
I installed 1.6.8 and also downloaded a set of programs from the vendor, Vilros, who sold the starter kit. I set up the first circuit and double-clicked on the file they provided, "circuit1.io". The circuit worked, flashing the LED at 1Hz. The IDE never opened, and when I click on the Arduino icon, I get a splash screen, "loading configurations", then no IDE. Nothing shows in the program manager either.
I uninstalled 1.6.8, installed 1.6.7, and the same thing happens. The weird thing is that even after restarting my laptop, which runs Win7 64bit, the circuit still works when plugged into the USB port. So the Arduino program is somehow still running even though I restarted the computer.
Nothing, I guess. So I thought I'd download the zip file for non-admin install, just for grins and giggles. It is currently coming in at about 40 kB/sec. My connection test at over 3MB/sec. This is incredibly frustrating. I really want to learn how to use an Arduino for improving my job skills, but I'm about to just hang it all up out of complete frustration.
Version 1.6.8 does install on an old Toshiba laptop that I keep around as a backup and for my grand-nephew to play Mincraft on. 64-bit Windows 7 and the install file worked perfectly and the IDE started without any problems.
I'm running Win8 / 64 bit and Win7 / 64 bit. IDE v 1.6.6 works on both; communication with board only tested on Win 8.
Some people say that the 'best' version is 1.6.5
Note: please give your question time to go around the world. People that might have the knowledge to answer might be sleeping at this time of the day. A general 'rule' for forums is to wait 24 hours before kicking your thread.
Thanks for the 1.6.5 suggestion, I downloaded that and it runs. At least I can see the IDE, I have not tried any programs/sketches yet, but I'm confident it will work.