well if you do not have the disc all most all factory built PCS have a built in recovery option to reinstall the OS to factory Default you could try that when you boot up your computer it should be like F12 or something you need to it it should be near the bottom of the screen your other option is to see if you can order a disc from microsoft sometimes if you have have a valid product key but no disc for around 30-40 bucks you can order a disc I think hope this helps.
Operating System Windows 7 Premium x64
Computer Type Desktop
OS Service Pack Service Pack 1
Internet Explorer Version IE 9
DirectX Version 11
CPU Type and Speed Intel Core i7 3770K @ 3.50GHz
CPU Cooling Water Cooling
CPU Idle Temp 28C
Motherboard Chipset Intel Z77
System BIOS Revision 1408
System Memory Type 16 GB DDR3 1600
Power Supply Unit (PSU) Thermaltake - 850-Watt TR2 RX Power Supply
Computer Monitor Samsung S23B550
Hard Drive M4-CT128M4SSD2 & WDC WD1002FAEX-00Z3A0
Optical Drives ASUS DRW-24B1ST & PIONEER BDR-207M
Keyboard and Mouse Logitech G510 & G500
Gaming Console Xbox 360
Anti-virus Software Bitdefender Total Security 2013
Productivity Suite Microsoft Office 2007
Computer Skill Level Self-Taught Expert
Windows Experience Index 7.8
Favorite Game Oblivion
Favorite Application CCleaner