Hi, I have a 5800 EM. I installed windows 7 7100 64bit a few weeks ago but only used my phone with PC again last week. I downloaded the latest OVI suite from nokia.com and when I first plugged my phone into the computer it took a really long time downloading and installing drivers (+- 15min) after that it seemed to work fine, connects to PC and I'm able to exchange files. I also updated my phone's firmware last week through Nokia Update Manager, no problems. I know that my phone's USB cable seems to be a bit fussy, so when it's plugged into the PC and connected I try to leave it absolutely still.
When you plug your phone into the computer, does it ask you how it should connect eg. PC suite, mass storage device or media player? Which option do you choose?