All my games are running slow

Hi,
Last week I was playing games normally, Skyrim on high and Garry's Mod too. From one day to another the games started running a lot slower so I had to downgrade to medium and skyrim is still unplayable because of all the lag. Does anyone know what the problem is?
Here are my specs:
Operating System:
Windows 7 Ultimate 64-bit SP1
CPU
Intel Core i7 2630QM @ 2.00GHz
Sandy Bridge 32nm Technology
RAM
6,00GB Dual-Channel DDR3 @ 665MHz (9-9-9-24)
Motherboard
Hewlett-Packard 1657 (CPU1)
Graphics
Monitor PnP Genérico (1366x768@60Hz)
Intel HD Graphics Family (HP)
1024MB ATI Radeon HD 6770M (HP)
CrossFire Disabled
Storage
223GB OCZ-TRION100 (SSD)
Optical Drives
hp DVD RW AD-7711H
Audio
IDT High Definition Audio CODEC