Hello Maggie and welcome to Seven Forums.
Couple of things you can try to solve this. See if you can access Safe Mode through the Advanced Boot Options menu. When you first power on your computer immediately start clicking the F8 key about once every second (top row of keyboard.) Keep clicking until the Advanced Boot Options menu appears. Use the up/down arrow keys to select Safe Mode and then click enter. Safe Mode
Once in Safe Mode you may be able to roll back your computer to a date/time prior to when this problem first occured by using a system restore point. System Restore
After rolling back your computer I would next check for any damaged or corrupt system files by running a system file checker scan from an elevated command prompt (option two.) If problems are found, run the scan 3 times and reboot your computer after each scan. SFC /SCANNOW Command - System File Checker
And don't forget to check for malware by running a full scan with your installed anti-virus suite.
has anyone any idea what i have done ?
It's hard to know what may have caused your machine to freeze. If you can remember what you were doing just before it froze that might offer a clue. Some possibilities include: Too many programs were open at the same time; insuffcient memory to perform a task; outdated drivers
; compatibility issues; malware; overheating; failing hardware; etc.
Please post back if anything helped or not.