You do need to do a clean install from the 10.7 recovery partition.
The following guide is for 10.6, but the same rules apply for 10.7 once you have booted from the Lion recovery partition.
To create a Clean Install (formerly known as Erase & Install) of Mac OS X 10.6 Snow Leopard (the 29 USD Upgrade DVD is a fully working retail version of Mac OS X and does not need a prior installation of Mac OS X on the Mac), follow one of the following guides:
- Short version: Clean Install of OS X 10.6 Snow Leopard
- Long version: Mac OS X v10.6 Snow Leopard: How to Erase and Install
OS X Lion: About Lion Recovery
Lion Recovery Disk Assistant
I guess, you haven't backed up anything before installing OS X 10.8 Mountain Lion?
i back up all the time, but the recovery partition is for mac osx 10.8 not 10.7. so how do i get the 10.7 recovery back
How do you backup? Time Machine or a clone?
And have you deleted the Mac OS X 10.7 Lion recovery partition? Normally when one installs OS X 10.8 Mountain Lion on a Mac with a Mac OS X 10.7 Lion recovery partition, one has two recovery partitions and two OS X partitions.
Maybe have a look at Advanced Search to find many similar threads about downgrading from OS X 10.8 Mountain Lion to Mac OS X 10.7 Lion:
im use time machine, and the only recovery partition is 10.8, i didnt delete the other one it seems as if this one has replaced it
Lion Internet Recovery
If you happen to encounter a situation in which you cannot start from the Recovery HD, such as your hard drive stopped responding or you installed a new hard drive without Mac OS X installed, new Mac models introduced after public availability of OS X Lion automatically use the Lion Internet Recovery feature if the Recovery HD (Command-R method above) doesn't work. Lion Internet Recovery lets you start your Mac directly from Apple's Servers. The system runs a quick test of your memory and hard drive to ensure there are no hardware issues.
Lion Internet Recovery presents a limited interface at first, with only the ability to select your preferred Wi-Fi network and, if needed, enter the WPA passphrase. Next, Lion Internet Recovery will download and start from a Recovery HD image. From there, you are offered all the same utilities and functions described above.
As with the Recovery HD, reinstallation of OS X Lion from Lion Internet Recovery requires an Internet connection. See "Supported network configurations and protocols" below.
Some computers that did not ship with OS X Lion installed may have a software update available that allows them to use Lion Internet Recovery.
What exactly is it that is crashing? Not many other people are complaining about significant amounts of crashes.
I hate it when people who don't know what they are doing fool around with betas and developer previews and then come screaming here when something goes wrong, very wrong.
This happens with every developer release.
Why on god's good earth would anyone throw a beta OS onto a perfectly working system?