The problem came from having Nvidia Optimus without the proper drivers. It was solved by installing the Bumblebee driver.
Booting from a live USB:
-2015/06/03 x86_64 ISO, tried both Torrent and direct download
-USB 2.0 flash drive, Toshiba TransMemory 8GB
-Booting on Toshiba Qosmio X70 (Intel Core i7-4700MQ; Nvidia GTX 770M; Intel HD 4500), which came with Windows 8.1 preinstalled. I have successfully installed Ubuntu 14.04 and Mint 17 and 17.1 previously, using the same USB drive as well. I am currently booting Windows 8.1 and Mint 17.1.
When I boot to the USB, everything’s fine at first. I’m able to reach the Try It or Install screen, and proceed from there. However, after a few minutes of Try It (regardless of what I’m doing), it completely freezes and I have to force shut down the computer. Additionally, if I try to connect to the Internet in either mode, it freezes as soon as I select the network. I’ve had the same problem in attempts to install several months ago as well.