I have a hp laptop with win 7. I want to remove win7 and install win xp. I tried booting form my xp cd but it shows no disk and have to abort installation. I don't want dual booting but just xp. So help me.

You need a valid Microsoft XP CD and you need to boot from it. Your "no disk" error, does it refer to your hard drive?

If this laptop came with Win 7 I would NOT recommend downgrading. It is very likely there aren't drivers for all your hardware under XP. Why would you want to do this anyway?

The laptop came with vista pre-installed. I upgraded to win 7, but as some of my softwares doesn't support vista or win 7 therefore I want to downgrade to xp

Upgrade to Win 7 premium which has legacy support for XP. If you still want to downgrade, first check to make sure there are XP drivers for your hardware. It sounds like your optical drive may not be supported.

All good answers, but none mentioned that Windows 7 preventds downgrade when you try to go back to install XP. So, you will have to wipe the drive first. You better have a complete XP installation CD in hand first, and a verified backup (or two) of all your files before starting.

Actually the most important thing to do is what ScottGem said. If the laptop came with vista loaded on it, you would want to check the manufacturer's site first to make sure that there are drivers for XP available on their site, otherwise the laptop will have extremely limited functionality when you load XP on it.

Agreed, upgrading and downgrading machines can be a real problem. While I like HP reliability, my experience has been that it is difficult to change operating systems with HP, due to lack of driver support. This of course, may be part of their hardware sales strategy. I used to buy buy a lot of HP equipment, but now, I just buy what's on sale at Best Buy. That may sound crazy, but if the manufacturers are going to treat computers as disposable, then so will I, and have no brand loyalty in the process. At least with Best Buy, if something goes wrong in my warranty period, they have replaced equipment with "equivalents" or better.

Lastly, I find that Windows 7 seems to do a pretty good job of running XP applications in compatibility mode. Sometimes the setup though is not obvious.