can some one please help my pc keeps freezing every couple of hours and some times restarts it self, also it some times takes ages 2 start up . the windows 7 start up logo will just freeze 4 ages??????

My Computer
- OS
- windows 7 32bit
- CPU
- AMD athlon(tm)IIx4630 processer 2.81ghz
- Memory
- 4.00 gb ddr
- Graphics Card(s)
- 1024mb Ati radeon HD 5450 pci-express vga card
- Hard Drives
- samsung 1tb