Hi Diviola, you have no choice but to buy a CD-ROM drive. They are not as expensive as you might think. You're windows CD can format the hard drive in you're computer before installing windows. Some people can use a USB memory stick but in order to copy the windows CD software to the memory stick you'll still need a CD-ROM drive. A 2GB or 1GB memory stick
will cost as much or more than a CD-ROM drive. Please click on the link to see some prices for a standard CD-ROM drive.
The link above is a CD-ROM drive & can also make CD-RW's (RW stands for re-write).
You can replace you're CD-ROM drive you're self. Just do not disconnect the cables from you're old CD-ROM drive untill you have the new drive. Connect the cables to the new drive (one at a time) as you disconnect them from the old CD-ROM drive.
Double check that the cables are tightly connected before you power up the PC. Load you're windows CD into the new CD-ROM drive & when you start you're PC up windows will start to load.
When you receive the new CD-ROM drive & if you need help connecting & running anything. You can come back here & ask questions. I'll help you through this.