Computer problems

Hey everyone
So lately my 5-6 year old computer Sony Vaio Pcv-RZ34G has been acting up lately. My specs are 1gb ram, 120gb hdd, ati radeon x700, 2.8ghz hyper threading and a 300watt psu. Everything started shortly after I got an error showing up when I started the computer saying my chassis fan was abnormal, I entered BIOS and went to Hardware Monitor and saw that the chassis fan was N/A and sometimes it would show me the rpm its spinning at. So I'm guessing that the fan stops and rotates again, I opened up the side of my PC and saw that the chassis fan did exactly that. stopped and spun over and over again. Also my comp has been freezing after startup leaving my keyboard,mouse, and everything else unusable he only way to shut it down is unplugging or holding down the power button. but my computer also works in Safe Mode everything functional. so my other guess was a bad driver thats been locking up my comp at startup. I also ran virus tests, registry cleaners and spyware removal. all came up empty. so that cancels out a virus making my computer unusable. I also think my PSU was been shot and not giving enough power to the fan but I don't know. I'm basically stumped. I did a test ladt night where I left my desktop running at around 11 last night and woke up this morning with the desktop still on but the time froze at 11:36 when it was clearly 9 in the morning. any help is appreciated thank you.

 

thats exactly what I did, I replaced the cmos battery and a new fan and the errors went away so far my comp hasn't froze and its been useable.