MTK6573 Handphone Dilemma

I desperately need help because i know that you all are my life saver. As it goes I'm having an unrooted chinese hand phone and there are no ways to root my phone other then to flash it. The dilemma is that i need to do a full backup before flashing but in order to do full backup i need to root it first but then i need to root it first before i can do a full backup. This is a dilemma sort like whether chicken or egg first. The problems is really annoying. BTW the phone download mode is not accessible through any combination of the phone button. Details are as follows:

Screen Size: 4.3 inch.
Model number: I9100
CPU: MTK6573
Android version: 4.0.9
Baseband version: I9100XXK13
Kernel version: 2.6.35.7-I9100
Build number: GT_I9100_01
Custom build version: 1341280728
ADB Devices: 0123456789ABCDEF

Are there any application that could do a FULL backup without rooting it first?
Does anyone knows where to download the said phone image file so that i could flash it without doing the full backup?

The last thing i could do is burying my phone in the soil and watered it everyday and hoping it to root out.
Thanks for your time in helping me out.

Physically the phone looks like Samsung Galaxy S2 and behave like one but actually it is a Chinese made clone. Pressing Power + Home + Volume Up will display an android with an exclamation mark. BTW i've tried all the combination of keys suggested from the webs but without success. Any clues?
Thanks for your time in helping me out.

— modified on Oct 12, 2012, 8:41:08 AM

Pressing Power + Home + Volume Down will start it as a normal start-up without going to download mode. I've tried it 3 times.
Any more clues?