Log in admin inconsitent after changing PHP version. (GoDaddy)

I’ll try to tell the story from the beginning as I’m not sure what could or not be related…
Am trying to install 1.5 on a domain I have no use yet, before I upgrade my live store from 1.38a
After uploading the files, changing confg, etc, I couldn’t access the install php (not found).
From old support files I learned that php needed to be upgraded from 4.49 to 5.3 and so I did.
This actually errored all my live sites offline ( Am using godaddy host account with sub host folders for each different domain) to make a long story short… fast forward few hr’s later,
I ended up adding the line (AddHandler x-httpd-php5 .php) to the .htacess file on my main host site and vwalla, everything appear again.
Very pleased, I Went ahead and installed the new 1.5, and everything seem to look fine, but I couldn’t log into the admin ;( after some more reading I cleaned cache, restart, and vwalla again, I log in and everything seem to work in the admin. crossing fingures, I tried to log out and then login again, using the same I.E browser but after I insert sn/pw and click login it will take me to domain/adminx/login.php?camefrom=index.php and give me file not found error. But if I just delete the login.php?camefrom=index.php and leave the http…domain/adminx and hit enter, I’m in the admin panel already!
Now if I try to log in with safari or chrome browser, it wil take me to another url domain/SUBFOLDER/adminx and also give me file not found error. (if I keep messing with the url I’ll sometime find myself in the admin area and somtimes redirect to the ?camefrom=index... Seem inconsistent.
I hope am making sense ?

I just wanted to add that my Zen Cart 1.3.8a working just fine without this issue.
Thank you so much.

Just to be clear, I had no progress with the admin issue of the 1.5 store.
I mantioned that the 1.38 working fine, because it might mean that this is not server issue. (I think)

If I can be honest with you.. I've read your post and I am not clear what the issue is you are having.. Perhaps others reading your post thought the same, and this may be why you've not gotten a response yet..

Can you state a little more simply what is the issue you are having..

Fresh copy of 1.5 installed.
When I log in the admin, sometime it will take me to the admin area, and other times it will give me "Page not found" Error.

I too don't understand what you're talking about. I can't replicate the problem either, despite trying lots of different things.

I suspect your problem is your server's confused PHP configuration. Get your hosting company to sort it out.

Thank you DrByte and diva. and Im sorry for my poor communication skills.

I ended up deleting this line from the htacess file, and it seem to solve the problems.

### re-direct index.php to root / ###
RewriteCond %{THE_REQUEST} ^.*\/index\.php\ HTTP/
RewriteRule ^(.*)index\.php$ /$1 [R=301,L]