If your PC is a little old, I’d be hesitant to upgrade from Windows 7 because you could run into problems with drivers. That said I upgraded my 8 year old laptop from Windows 7 to 10 and managed to sort out the drivers after a bit of work, but it wasn’t worth the effort and time. You could wait till 2020 when support for Windows 7 ceases, then you have little to lose, bit I suspect you’d be ready to upgrade the hardware by then
Certainly, bbunge’s advice on the browser cache and cookies is well worth a try. Failing that, just stick with IE for the webui, and then try Firefox and Chrome again in a few weeks, after new updates are out.
However, if you want a distraction from all the Christmas and new year tv and frivolity, upgrade to Windows 10, but don’t forget to properly back up any documents etc you can’t afford to lose. That’s assuming you can get Windows 10 for free, and that you have an OE version of Windows 7 with a licence number. If you have to buy Windows 10, the Christmas tv is by far the better option.