Ok, then the steps should be as illustrated in the article.
You are positively certain that you have disabled the HTML editor? Because the only thing I can think of that will mess with the HTML is if the HTML editor is enabled.
Perhaps if you don’t have administrator privilege that may also cause problems.
One of the driving philosophies behind Joomla! is security. They try very hard to disallow anything that might compromise the security of the system – which is why certain HTML tags are automatically stripped.

im using 1.5,please

With Joomla! 1.5 it is simply a matter of disabling the HTML editor – as in steps 1 – 3 above.
Unfortunately, the instructions are slightly different for other versions of Joomla!
If you are using a version of Joomla! other than 1.5, please check out one of the following articles:
If you are using Joomla! 1.6, the instructions can be found here.
If you are using Joomla! 1.7, the instructions can be found here.
If you are using Joomla! 2.5, the instructions can be found here.

I am no conversion expert (converting visits to ad clicks), but … here are my thoughts and observations:
Looking at your site, the biggest problem I see is that you have no content, no original information. You simply provide links to other sites. Most visitors leave these kinds of sites in a hurry.
You have to try and think like a user or visitor to your site: What are they looking for? They are looking for information. They type a query into a search engine (usually Google) and your site comes up. They expect their query to be answered on your site – not to be redirected somewhere else.
There is no problem with providing a one stop collection of links to Bangladeshi newspapers – it is a wonderful convenience to have them in one place, but that is just one page – not a whole site.
If you want this to be the model for your whole site, then you have to think about designing your site as a portal or gateway to Bangladeshi newspapers.
As for advertising revenue … well, again, think as a user or visitor: Did they come to your site to check out ads or to check out content? – They came to check out content. For most people, ads are just annoying.
Every once in a while, somebody might find an ad of interest and might click it. But how many people do that? Unfortunately, Google doesn’t allow people to talk about numbers when talking about Adsense, however, use your own web browsing habits as a guide.
Myself, I rarely click on ads. I go months without clicking on ads (and I, generally, browse over 100 pages per day). However, when I am looking for something specific (say an ARM SBC), as well as clicking on site links, I might click on related ads.

Thank you for your feedback.
My instructions were incomplete and would lead to your problem. They have now been updated.
The problem was that HTML filtering has to be disabled for you to correctly add Adsense to your site.
As well, I created a seperate article for Joomla! 1.6 (since the process is a little different).