Android wont turn on after installing App

[paddyirishman]

I installed an app on my Samsung GT-15800 last night before going to bed.
Unfortunately I cant remember the name of the app but it replaced my home screen interface. Seamed pretty decent but I noticed a slower operation speed.

This morning my phone was turned off (my battery died even though it was fairly charged the night before) so I plugged in the charger.
When I tried to turn on the phone, the Samsung loading logo (pulsating) appeared as normal, but the phone wont boot past that point. So I cannot access my phone.

I've tried simple things like removing battery & memory card, but none make any difference. My phone has now been turned on for about 2 hours and I still see the loading screen.
Would anyone know of a fix for this or what I could do to access & use my Android again??

I've noticed on this Forum people have had similar problems, one such suggestion of a fix was posted by 'brynneada' in this thread. She says:

Power down the phone and download and extract this to your desktop MetroStockRecovery-SCRIPTS.zip after you done that press and hold vol down, end key and power, your phone should be on the white huawei screen and it should stay there plug your phone to the computer via usb cable, now open the folder that you extracted and run both of these file, first run fastboot-windows you will see a black box come and leave quick, next run metroPCSStock-windows.bat than another black box will pop up and it will do its thing, once it finishes the phone will automatic reboot itself.

Is this programme safe? will it totally reset my phone? and I dont have an end key, so do I use the back, menu or home button?

Really appreciate any help you may have, as I was late for work today 'cous my alarm didnt go off gurrrrrr....

Thanks