The problems sound a bit like network issues so I would rule out the obvious:
- If you use wireless connection try with a wired connection.
- If you use wired connection try replacing the cable (the cable might look fine to eye but it can easily have damage from eg. if the cable had too tight loops etc).
- If you use wired connection try with a wireless connection or another network card.
I assume other network stuff in your household remained the same so the problem, if it is network related, is likely in the upgraded computer so trying to rule those out would help.