Is this a PSU problem?

Hi guys

I have been having a little problem for a few weeks. Every now and again my PC has been freezing for a few seconds at a time. I had formatted and installed a fresh copy of windows maybe a week or so before this started to happen so i assumed that this is likely to be a hardware issue (i had a PC overheating a few years ago and it did a similar thing)

Before opening it up i tested my hdd with seatools and tested my RAM with ultimate boot and they both passed. ASUS probe tells me that my CPU temperature is fine too.

I opened her up to check the CPU cooler and to remove any dust as i thought it could be possible that this might be affecting the fan. There was a little bit but not really much at all. I started her up with the side panel still removed and all seemed fine again. When i replaced the panel the problem returned. I've been using it without the side panel on without any issue for a while but the problem has started to resurface.

All the components are about 2 years old except for the case and PSU that I got from a mate as I didn't have much cash to spare at the time. It looks like a nasty £10-15 jobbie so probably not much cop.

Does this sound like a PSU problem to anyone? Or any other possible problem?

I have been thinking of upgrading my system so if anyone could recommend a decent PSU I'd be happy to hear any ideas. I would be thinking of spending about £100 for a PSU and a case. Would be looking at keeping the m/board and CPU cost as close to £200 as possible. Have been looking at the intel i3 maybe stretch to an i5 with an asus board

Thanks in advance
moo