Wireless connection dropping

[#1]

We recently changed from Thomson Speedtouch 330 broadband connection to BT 1800HG wireless connection as a result of contacting Plusnet for a MAC key and being talked into staying put. The problems are:
1, Since connecting to the wireless router we are getting constant drops in connection despite the wireless connection telling me it is connected and has excellent signal strength.
2, Unable to send or receive email through OE although it can be retrieved through Plusnet portal.
3, Incredibly slow browsing (virtually Dial-up) speeds. This may well be due to a change in our broadband package at the same time as changing to wireless, which I am now regretting.
I have moved the wireless landline phone away from the same socket as the router, although its still in the same room.
Although now wireless the PC is still located where it can be wired so I am now wondering about switching back to wired to save all the hassle, is this an option? Can you have a wired and wireless connection at the same time? to allow you to switch between them?
As you can probably tell I'm not all that clued up on this subject.

[#2]

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Can you have a wired and wireless connection at the same time? to allow you to switch between them?

You can quite happily have a combination of the both; I always opt for a wired connection if possible and use wireless only where necessary.
Do you just have the one wireless device?
If so do you have another wireless adapter you can try?
Also do you have any of the following; neighbouring wireless connections, bluetooth devices, DECT phones or wireless video senders. All of which can interfere with a wireless connection.

[#3]

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it is not advisable to attempt to connect the same device by both ethernet and wireless at the same time

Apart from the computer being assigned 2 IP addresses (which I have never had problems with) why would this be a problem?

[#4]

I imagine (I'm no expert here) that the differences in recommended MTU for wired and wireless connections may play a part.

[#5]

Are the MTU type settings relevant when it comes to local connections whether they be wired or wireless. I thought they were altered only on ADSL connections.

[#6]

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What error message are you getting in OE?

Error 678 No Dial Tone. Think i have solved this one now thanks.

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Which package are you now on?

Changed from Broadband Premier to  Broadband your way option 2
BT speed test result:
Test1 comprises of Best Effort Test: -provides background information.
IP profile for your line is - 6500 kbps
DSL connection rate: 448 kbps(UP-STREAM) 7616 kbps(DOWN-STREAM)
Actual IP throughput achieved during the test was - 3563 kbps
Other speedtest
Download speed 2583kbps
Upload speed 378kbps

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Please can you post your router line stats (log on your router 192.168.1.1 and there should be a ADSL status page), in particular your upstream and downstream sync speeds and your SNR margin.

Sorry I don’t understand this, and I get IE cannot display the webpage.

[#7]

The Ethernet connection seams to have solved all speed and connection problems and have got OE working again too. Although this does not resolve the wireless issue I don't really need to be wireless as yet so I will deal with that should I need a wireless connection in the future.
Thanks for all your help.