Cellular is normally susceptible to the local tower's ability to the load incurred. So for example during rush hour when everyone is on the cell phone saying they are on thier way, the speed of the 'network connection' slows down due to the load on the network (I watched it here happen especially when a accident slow / shut down lanes, OMG!).
That said there is any number of other issues this can be inclusive to the USB cellular modem just being shoddy (yes they always say it is your PC that is the problem because 90% of thier callers are people whom dont' know what a Motherboard is and mess thier computers up). That you did something to 'turn off' sounds like your computer is trying to be online to do all the tasks it is supposed to, but your bandwidth isn't big enough anymore to support a modern computer (which is typical and common because ALOT of stuff on your PC 'needs' to constantly check on the Internet for things). From my myriad of different experiances, unless you were desperate, I wouldn't dare rely on a CellModem as the 'main' Internet source. Among the various free HotSpots that exist at McDonalds, Starbucks, Libraries, Internet Cafes, and so on, there is plenty of places to 'plug in', otherwise for home use I would seek either DSL, Cable, or a Microwave shot, before I would go Satellite Internet (also a option).
Let's start with some basics. First download SPECCY and run it, copying the first tab info and provide it here so we know what we are dealing with.
First what antivirus do you have? Free or Payfor? If you have none, go to www.filehippo.com and download AVG or AVAST! and do a full scan. Second download and run Malwarebytes, again full scan. Makes sure these both come up completely clean they look for different things and take a while to do the job.
Next go to the Orb and type Windows Update, complete all updates and options, except BING. Once that is done then download and run SlimDrivers, install all drivers but don't reboot till the last driver is done installing.
Now we know the system is clean (reason for it doing things that can slow things down) and upto date (another reason to slow things down), let's make sure it doesn't have things it doesn't need to run. For example if it is constantly trying to pull Adobe Reader's update, but you have such a slow connection, then it will take forever before it can complete. Download
http://www.sterjosoft.com/startup-patrol.html and DECLINE the last two screen on the install, you will then find it running in your system tray. Double click and start going through CAREFULLY what shouldn't be running 'all the time' (startup), for example Adobe Reader, or Java Update. If something is unfamiliar then look it up before doing anything with it. This will clean up the programs 'starting up' which normally (as noted) go online to do 'things'.