Odd router problems - help appreciated!

[#1]

Hi all
Since I got a new router (Thompson one) I am having real issues uploading photographs and documents to Hotmail and a couple of other sites. The upload seems to 'time out' and the issue comes up that I'm not connected to the internet.
Plusnet say there is nothing they can do as there doesn't appear to be a fault on my line - but my old router didn't have this issue (a BT one).
I have tried 2 routers now without success. I also tried different browsers. Initially I was able to undertake the tasks I needed with Firefox (my default is Internet Explorer) but now the same 'timeout' problems are occuring (that and I've been kicked offline repeatedly!).
I know it is a problem with my line or router, as I can undertake the tasks no problems using mobile broadband.
I haven't changed anything on my computer; the only difference is the router.
If anyone has any advice it would be greatly appreciated! I have asked Plusnet if they can send me a different router; has anyone else had problems with the Thompson router?

[#2]

Are you connecting to the router wired or wireless?

[#3]

Thanks for your reply. I am connecting normally via wireless but when I have tried being plugged into the router also there is still no change. There isn't enough 'power' for me to complete a speedtest at speedtester.bt.com either as requested by Plusnet!

[#4]

What are the full model numbers of the routers you have tried which do and don't work ?

[#5]

Try setting the router "MTU" value to 1458 and see if that makes it better, if it does then there are further optimizations to be done.

[#6]

Thanks for the replies. How would I change the router MUT please?
The router is a Thompson TG585V8. The old one was a BT Touchspeed one I think.
I have just tried using a different machine on the network and this works alright. So it appears to be something in my machine's settings which might be the problem. What on earth could it be? I haven't changed anything.

[#7]

Can you perform a speedtest at mybroadbandspeed.co.uk so we can see the upload speed?
Are the pictures high quality (on my camera they can be several meg so can take a while to upload).

[#8]

Sorry for the delay in responding. Things have got worse, it won't work on either machine now nor does it matter what browser I use.
Some pictures are high quality, some are just taken on my phone. I don't mind if they take a while to upload, but it's like it starts to load and then goes "nah, can't be bothered" and drops the connection. Other pages are dropping connection too - hotmail, for example, often does that "Hotmail cannot connect at the moment" thing it does when it loses internet connection. Yet Plusnet say that they cannot see that at at any time my connection is dropped.
I tried a speed test at the site you recommended and the speeds are 2038 download and 376 upload.
I have no idea what to do beyond buying a new router, but if that doesn't work either that would be a waste of money.