iMac won't upload anything. Please Help!!

Is your iMac connected via WiFi or wired Ethernet?

If one, try the other. If wired, you should try a new Ethernet cable straight into your cable modem or DSL modem. Eliminate any device you can (e.g. router).

 

Is 0.50 Mbps what you expect from your Wifi network?

So, to sum up:
Macbook -> Wifi = works fine
Macbook -> Hotspot 4G = works fine

iMac -> Wifi = doesn't work at all
iMac -> Hotspot 4G = doesn't work at all
iMac -> Ethernet = works fine

Is that correct?

If so, it points to some issue with your iMac's Wifi. No idea what this might be. I've never heard of the Wifi chips going "bad" or anything like that. Could be some kind of strange software issue, I suppose. But again, I'm not familiar with such an issue.

I would say that it could be a problem with your router configuration, but since your 4G hotspot doesn't work either, it kind of rules that out.

Sorry I can't be of more help.

 

Yeah, it's confusing.

Could be a Wifi issue with the iMac (which has an airport card, I believe). But the tethering problem and the (brief) clean install success puts that in doubt.

Could be a router problem, but the Macbook Wifi success puts that in doubt.

Could be wireless interference if you live in a crowded apartment building, but Macbook Wifi success puts that in doubt.

Could be a weird software issue. The clean install working then turning sour could support this, but it's hard to say.

Things that I would try:

a) Uninstall any and all third-party networking software you have, such as the HoRNDIS product you mention above. Do another clean install if you have to and install nothing else until you are able to fully test the Wifi.

b) Try a different wireless router. They can vary widely in performance and compatibility. Borrow one or buy one from a place with a generous return policy. Since you have Macs, I would recommend an Apple Airport Express (or Extreme if you have the cash for that).

c) If nothing else resolved the issue, then I would start thinking about cracking open the iMac and replacing the Airport card inside. If you have no or little experience working with the guts of computers, DO NOT DO THIS. I've opened a lot of Macs in the past, going back to the original Bondi Blue ones, so it's a possibility for me.

If I were to bet, I would bet on (a) being the problem. The fact that only upload is affected sounds like a weird software issue. The fact that your Macbook Pro works seems to rule out wireless problems outside the iMac.

Good luck!

 

I thing I like about troubleshooting is isolating one part. if you have the time install Windows, and try to upload something.

At least then you know it's a problem within OS X, and not your WiFi Chip.

 

4G driver might not be compatible with the hardware in your iMac. What year is your laptop?

I had a 2009 iMac that stopped working with my router after an update before (ethernet and wifi). It turns out it was a driver update I installed, that was not compatible with something inside the Belkin router I was using. I ended up buying an airport extreme.

Me thinks it has to be something along those lines.

try rolling back to an earlier version of OS X 10.9

 

I was about to suggest to debug the router.
What router do you have? - do you have a second one to test?

Option click on the WIFI icon in your iMac's toolbar - what are the RSSI and transmit rates?

Use a program (money) like iStumbler or WIFI scanner to see if there is interference on the wifi band you are using.
Check if the channels you are using are crowded by neighbors - if so change them.

If that does not help you might do the clean install - don't install and then restore from backup etc!

Check after the clean install what the upload/download speed are - use http://www.speedtest.net for example.