broadband connection issue (internal lan)

[#1]

Hi
I have just bought a new PC so I decided to give my old one to my other half.
however it has developed a connection issue that I can not work out,
it is desperatly slow when you go online ( can't even complete  a speedtest) stops you tube vdoes at 20-30 seconds and wort continue and takes ages if you try to download anything.
it's not a fault on the lan cable as i have swopped these around onto my other pc's and speed / download is fine.
the pc in question is running windows vista and is a intel quad core q6600 with 4 gb ram , using either fire fox or IE makes no difference.
anty help would be greatly apreciated..
steve

[#2]

Have you tried with the security software disabled
Have you checked speeds when copying a file over the network from the new computer
Moved to Windows as it doesn't really fit under broadband and routers

[#3]

Quote from: Oldjim

Have you tried with the security software disabled

Just as relevant, have you run a virus scan?
[Moderator's note by Dick (Strat) Quote fixed.]
[color=teal][User's note by walker23. Missing moderator's closing square bracket fixed]
Thanks for correcting it Strat, I really should preview or check more often.

[#4]

Quote from: Oldjim

Have you checked speeds when copying a file over the network from the new computer

tried this today a 875mb video took 16 mins to transfer, that doesnt sound right, does it?

Quote from: Oldjim

Have you tried with the security software disabled

had a busy day havn't got round to tryimg this option.
thanks  so far
steve

[#5]

The router LAN is normally limited to 100Mbps
The speed you got was 7.29Mbps