First of all do not expect slim console flashing to be a walk in the park like the older fat consoles...
secondly
post your console MFG date ... and open up the xbox to find the revision of the drive ....do the following
.) if its the older 9504/0225/0401 drives(which i doubt since these were last found in console MFG August 2011) then you can Mod it using a dremel Drill and xbox360usbpro(Costs 70 dollars)
.)newer lite-on 1175 and HL 0500 slim drives cannot be modded unless you replace the internal PCB which costs nearly 80 dollars(you need basic soldering skills for this) ... LTU PCB
.) to flash these LTU PCBs you need xbox360usbpro ... No SATA chipsets will work like in the old days ... this gadget costs around 70 dollars
.) you need CK3 power kit to power the LTU PCB in vendor mode ... costs another 50 dollars....
so you will have to spend nearly as much as on a new xbox for the flashing kit and then you need some soldering skills to replace the PCB and then use a PC to flash the replacement PCB
the other option is to RGH the console and replace the dvd drive with that of fat console .. that requires Professional Soldering Skills..