Jap, maybe you have the ability to hang another computer on your internet connection to see if it is the computer or your router/isp? or vice versa, you could also hang your computer on another connection to see what happens.
I get a feeling that it has something to do with the update and / or perf beta. did you update from 1.3 or did you install 1.5? here could be the problem somewhere ...
it could be a performance problem ... maybe your graphics card or your cpu will be too hot or overload. it could also be a memory problem.
but it could also firewall, router, cable, antivirus, proxies (if used), other programs, driver problems or anything. Therefore, it would make sense step by step to narrow down the error.
that could take some time ...
if you have no other Internet line or another computer available I would perhaps completely uninstall PR once and reinstall 1.5.
but before I would delete all (!) settings and only when it is running and the error is fixed copy them back.
if you need help to find the hidden folders of pr, let me know. there are still some data hidden in system folders of windows ...
edit: have you ever defragmented your hard drive?