connection impossible, only 1 in 10 attempts is successful

I often use the program WinSCP to connect my home PC with my job network. Since I bought a new PC with Windows 7, the connection is almost always impossible. On average, only 1 in 10 attempts is successful. I confirm that when I was using the old PC with XP or another PC with W98 the connection was always guaranteed. What does it depend? how can I fix it?
Franco

Do you have the problem with WinSCP only or with other clients as well?

Sorry if I answer in a long time, but now I just need to use WinSCP. I suppose that the fault depends on Windows 7 because there is another PC with XP connected to the same router and it works properly. I confirm that I have checked the firewall to open the connection to WinSCP. What I had to do?

Can you answer my question in the previous post?

@IW5EIK: I use Windows 7 and hadn't any problem for now (which isn't also present on XP etc.)

Did you tried to run it with admin rights?
Have you UAC enabled? (I didn't)
Which firewall are you using?