|"The recovery disk doesn't work as the repair place also merged two drives ..."|
All drives in Windows are logical drives, but logical is omitted.
A single drive letter is assigned to CD or DVD or floppy drives, but other things can have more than one drive letter assigned to them, if they have more than one partition. A hard drive can have more than one partition, and each partition can have it's own (logical) drive letter. Brand name systems usually come with two partitions on the single hard drive. You often can't see the second partition in Windows in My Computer or Windows Explorer, because that's what the brand intended, but it can be seen when the operating system disk is used to boot the computer.
If you have only 1 hard drive, the techs probably deleted both of the original two partitions on the one drive before they installed Windows.
There are three types of Recovery disk scenarios.
This is probably your scenario...
For the first scenario, a Recovery program on a single Recovery CD uses the data that's already on the second Recovery partition on the hard drive (that was put there by the brand name before you got the computer) to reload the contents of what the brand originally installed on what you see in Windows as the C partition.
The hard drive MUST still be okay.
If the second partition has been deleted to allow Windows to use only one partition and all the hard drive's space, or if the data on the second partition was altered, or if the original hard drive has failed and been replaced, that type of Recovery disk can't restore the original data contents.
For the second scenario, a Recovery DVD or a Recovery CD or DVD disk SET allows you to re-load the entire hard drive with it's original two partitions and all the data on both partitions. You don't need to do much yourself except insert another disk when prompted, if there is more than one disk. You need that to load the orginal brand name software installation on a blank hard drive, such as when the original drive failed and you had to replace it.
If that DVD or disk SET did come NOT with your computer, usually you were supposed to make such a Recovery DVD or Recovery disk set yourself, using a program provided by the brand name that was already installed, while Windows is still working properly.
If the computer is not more than 5 yearsold or so, if you didn't make the Recovery DVD or disk set, you can often order it from the brand name's web site.
For the third scenario, you may get a single DVD or CD, or two of them, when you get the computer. The first disk is an operating system re-installation CD or DVD - it's almost the same as a regular Microsoft Windows operating system installation disk. You see the same things, have to supply the same info, as if you were using a regular Microsoft disk to install Windows. You are not prompted to insert another disk when Setup is finished. If you get another CD or DVD, that has the drivers needed for the system, and possibly Applications - programs not built into Windows that were included with the original brand name software installation. You use that second disk to install the drivers the system needs, and if applicable and you want to, the original Applications.
If that DVD or disk SET did come NOT with your computer, there is usually no program program provided by the brand name that was already installed, with which you can make the disk or disk set, while Windows is still working properly.
If the computer is not more than 5 years old or so, you can often order the disk or disk set from the brand name's web site.