Try the volume buttons until you get Start or Android or something like that. Then tap the power button. If it boots back into the bootloader (what you call fastboot mode), find a recent ROM for it, extract the bootloader.img file and use fastboot (on a PC) to boot the image. (You'll have to have the Infinix driver installed on the PC.)
fastboot boot boot.img
If that gets you back to normal, go back to the bootloader:
adb reboot fastboot
then issue
fastboot flash boot boot.img
When that's done, issue
fastboot reboot
and you should be back to normal.
If booting the boot.img file doesn't work (you'll get back to the bootloader), you have no Android (or apps or pictures or anything) on the phone, and you'll have to reflash the ROM. (Ctrl-F and search for hot 4 - there are 3 hot 4 pro models, choose the correct one. Click the "See instructions" link and follow them.)