Once you install stock as above, go ahead and test internet ... use facebook, post some instgram photos, et cetera. If that goes without issue, then the problem lay with the software. If it still turns off, then your phone will need servicing.
If it is a software issue, there's a slim if any chance that loading a ROM will continue the good luck. The only chance is if the problem was a bad setting in userdata that stuck around between flashes (that is, if you didn't factory reset between using Cyanofox and trying CM (and other ROMs).
Sent from my MyTouch 4G Slide using XDA Free mobile app
Primary Phone: HTC MyTouch 4G Slide (Doubleshot), S-Off, running CyanogenMod 10.1
Backup Phone: Samsung Infuse 4G (i997R) running Beanstalk 4.4+
On Order: LG Optimus F3Q, running stock