Google Instant which automatically shows search results as you type may not show you search results while are you typing there are many reasons for this, let us see some of them.
Reasons for results not appear from Google Instant as you type
1.If Google Instant detects slower connection on your side then Google Instant will be automatically turned off and Google does suggests you to use normal search by pressing enter.
2.Google Instant also block listed some queries which are of pornographic type, so for these sort of queries Google suggests you to enter to perform search.
3. You need to be searching from Google homepage only.
4.Search from your iGoogle page, Google SSL will not offer search results as you type.
5.Google Instant supports browsers,Firefox 3.0 or higher version,Safari 5 for Mac and later version,IE8,Google Chrome 5 and later versions only.Check to see if you are using any of these browsers.
Google Instant does not support Opera, read
6.You have previously disabled autocomplete feature.
7.You previously opted out of Google Instant.
8.You use a Google domain or interface language that does not yet support Google Instant.
via [Google Help]