Broadband speed running at 400kbs---HELP!!!!

[#1]

Hi, just set up my broadband today for my new laptop and can connect ok. However, it seemed to be running very slowly so took the Plusnet speedtest which said it was downloading at a measly 400kbs.
I was not expecting 8000kbs but would have even been happy with 3 or 4000 download speed.
Can anyone from Plusnet or this community please advise what I should do.

Thankyou

[#2]

Oh, forgot to add there is no issue with overuse of bandwidth as I am a new customer and only connected for the first time today via the modem that came with my Plusnet broadband package.
As I was having a few problems setting up the wireless connection, I am now connected by the supplied cable direct from the modem to my laptop.

Thankyou

[#3]

Just tried running the BT line tester and after entering my phone number it asked for my normal log in name.
I tried with my registered plusnet log in name as well as my full plusnet e mail address but each time it came up with an error message saying:
"
The login name entered on this tool doesnt match that discovered by querying the network for your domain name. Please check your telephone number (or user name) and try again. If problem persists please contact your CP. "
What should I be entering in this box please? Should I be entering something else other than the two ways of logging in previously mentioned?

Thankyou

[#4]

The login name required by the BT test is the same one you enter into your router username@realm, so username@plusdsl.net for PlusNet.
To enable users to offer help with your speed problem you need to post the stats from your router, sync speeds, noise margins and attenuations.  If you are unsure how to get that information check this page on Kitz's website.
It would also help if you mentioned the router make and model.