Outlook problem when downloading

Hello,
Recently, when I open outlook, to download my email, I keep receiving the last five mails I was about to receive normally. However I am unable to recieve the rest, as the download is "sticking" at message 13....as if it is such a huge file I can not receive it.
This then blocks any other mail to be received to my outlook mailbox. I now have over 150 mials sat there waiting.
My processor goes into over drive and I have to totally close the program, to slow down my processors.....
Done update and virus checks and all that.

Any advice would be appreciated.

Phil