Every time I download a video it stops every few seconds

The cause of your problem is simple: your "cache"
memory & "temporary internet files" are nearly full.
This is especially true if you've been watching lots
of videos or playing a lot of games/music.

If you are experiencing either: A) slugglish loading
and buffering, B) "choppy" videos which frequently
start/stop/start/stop, C) the YouTube dotted circle
looking like it might spin for ever, or D) videos that
will sometimes come to a sudden "stop" or freeze,
that is often a sign that your cache/memory is full
and cannot take anymore.

Exit out of YouTube (but not your browser) and do
one of the steps below. Afterwards, shutdown and
reboot. Not only will this "free up" your computer's
memory, everything will be "fresh", and load faster:

Internet Explorer 6:
→ Tools → Internet Options
→ Delete Cookies → OK
→ Delete Files → OK
→ Clear History → Yes
→ OK

Internet Explorer 7:
→ Tools → Internet Options → Delete...
→ Delete files → Yes
→ Delete cookies → OK
→ Delete history → OK
→ Close (browsing history window)
→ OK

Internet Explorer 8:
→ Tools → Delete Browsing History
[. ] Preserve Favorites (leave blank)
[x] Temporary Internet files
[x] Cookies
[x] History
→ Delete

Mozilla Firefox 3:
→ Tools → Clear Private Data
[x] Browsing History
[x] Download History
[x] Saved Form and Search History
[x] Cache
[x] Cookies
→ Clear Private Data Now
Google Chrome:
→ Tools (wrench) → Clear browsing data...
[x] Clear browsing history
[x] Clear download history
[x] Empty the cache
[x] Delete cookies
Clear data from this period: → Everything
→ Clear Browsing Data

Please rate me if this solution works for you

Thanks......Have a great time.