Been on fibre nearly a week and...

[#1]

I noticed pages not loading correctly in IE which loaded fine under adsl2. Strange is though the same pages load fine in Safari. Youtube in IE doesn't load right, a lot of the thumbnails end up being Xs and I can't get the picture to load.
Do I need to reinstall Windows?

[#2]

Have you tried clearing your cache? Could you try another browser like Chrome to see if that has the same issue?

[#3]

Also check for any extensions that could be affecting things.
Nothing should have changed as the result of a change from ADSL to fibre.
You certainly should not need to reinstall Windows.
Is your IE itself up to date?  Even if not it should not have that effect.  IE/Youtube/PlusNet fibre working fine for me.
Did you mean Safari on your Windows machine?  Be a little careful with that as Apple are not fully supporting it any more.

[#4]

Had to switch to Firefox.

[#5]

If you are using the Plusnet Router and Openreach Modem it is just possible that using the Plusnet DNS server specified by the Router may some how result in some pages either loading incompletely or stalling - see the thread "Web Pages stall when loading" - for some information about this. It is not a universal problem but several users report having had the problem.
If the problem persists try changing the preferred DNS servers on your PC to OpenDNS numbers  (Primary: 208.67.222.222  Secondary: 208.67.220.220) - it may help. It certainly helped me both when using my Mac and when using my Windows Laptop. Its easy to change back and it doesn't involve getting into the router using Telnet commands or doing anything complicated.

[#6]

This type of issue could be caused by packet loss, but there's a couple of other things we can look at.
If the problem continues can you try opening whatever site if affected in Firefox and then pressing CTRL+SHIFT+Q - this brings up some tools to look at what's going on. In here we're looking for where there are timeouts when trying to retrieve elements of the page, or maybe 404 errors or even DNS lookup issues.
If possible it'd be useful to see what's happening via a wireshark capture, this lets us see whether the issues are caused by DNS fails, TCP fails, packet loss etc.