Can No Longer Upload Large Files

I usually send clients large images around 4Mb via the email. I also upload to various sites, files up to 15Mb. They are all usually jpeg or .psd format.

For some reason it just doesn't work anymore - they get so far and seem to just hang. I contacted my ISP provider and they went through all their trouble shooter but told me that the problem is my end.

I am using Windows 7 64 bit. I have tried IE9 and Google Chrome but neither helps. I use Microsoft Security Essential. I have tried turning off the firewall but this doesn't work either.

Smaller versions of the jpegs seem to upload OK. I haven't done anything to change what I am using recently other than to run the automatic updates.

I have internet satellite using an ipstar modem. No router.